From ade634a690e3b489df1f5ad8624595eaabdb06d9 Mon Sep 17 00:00:00 2001
From: Tommaso Bonato <tommasobonato95@gmail.com>
Date: Tue, 10 Feb 2026 16:46:19 +0100
Subject: [PATCH] Add comprehensive test suite for all topologies
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Four test scripts covering 126 tests total:
- run_all_tests.sh: 22 functional tests (DF/SF × 4 routing × 1/10 flows)
- run_reachability_tests.sh: 18 reachability tests (one-to-all, all-to-one,
  same-switch, cross-group/partition, max distance)
- run_edge_case_tests.sh: 49 edge case tests (cwnd/queue variations, tiny/
  large flows, incast/outcast, staggered starts, cross-topology consistency)
- run_e2e_tests.sh: 37 E2E stress tests (bisection, permutation, 1024-node
  FT, 1134-host SF p7q9, heavy incast, mixed sizes, all routing combos)

All paths are relative (SCRIPT_DIR-based) for portability.
Generated TM/output files excluded via .gitignore.
---
 tests/.gitignore                |   8 +
 tests/run_all_tests.sh          | 254 +++++++++++++++++
 tests/run_e2e_tests.sh          | 415 ++++++++++++++++++++++++++++
 tests/run_edge_case_tests.sh    | 474 ++++++++++++++++++++++++++++++++
 tests/run_reachability_tests.sh | 313 +++++++++++++++++++++
 5 files changed, 1464 insertions(+)
 create mode 100644 tests/.gitignore
 create mode 100755 tests/run_all_tests.sh
 create mode 100755 tests/run_e2e_tests.sh
 create mode 100755 tests/run_edge_case_tests.sh
 create mode 100755 tests/run_reachability_tests.sh

diff --git a/tests/.gitignore b/tests/.gitignore
new file mode 100644
index 0000000..0dea38f
--- /dev/null
+++ b/tests/.gitignore
@@ -0,0 +1,8 @@
+# Generated test artifacts (created at runtime)
+*.tm
+*.txt
+*.dat
+edge_tms/
+edge_out/
+e2e_tms/
+e2e_out/
diff --git a/tests/run_all_tests.sh b/tests/run_all_tests.sh
new file mode 100755
index 0000000..3b6e6d5
--- /dev/null
+++ b/tests/run_all_tests.sh
@@ -0,0 +1,254 @@
+#!/usr/bin/env bash
+# Comprehensive topology & routing tests for HTSIM dragonfly and slimfly
+# Verifies: (1) all flows finish (2) retransmission recovery (3) expected runtime
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
+HTSIM_DIR="$REPO_DIR"
+UEC_BIN="$HTSIM_DIR/htsim/sim/datacenter/htsim_uec"
+TOPO_DIR="$HTSIM_DIR/htsim/sim/datacenter/topologies"
+TEST_DIR="$SCRIPT_DIR"
+
+PASS=0
+FAIL=0
+TOTAL=0
+
+# ============================================================
+# Traffic matrix creation helpers
+# ============================================================
+
+# Create a single-flow TM: src 0 -> dst <last_host>, 1 MiB
+make_single_flow_tm() {
+    local num_hosts=$1
+    local outfile=$2
+    local dst=$((num_hosts - 1))
+    cat > "$outfile" <<EOF
+Nodes $num_hosts
+Connections 1
+0->$dst start 0 size 1048576
+EOF
+}
+
+# Create a medium TM: 10 random-ish flows across different switches, 1 MiB each
+make_medium_tm() {
+    local num_hosts=$1
+    local outfile=$2
+    local p=$3          # hosts per switch
+    local num_flows=10
+    
+    # Pick flows that span different groups/partitions
+    # Spread src and dst across the host range
+    local step=$(( num_hosts / (num_flows + 1) ))
+    [ "$step" -lt 1 ] && step=1
+    
+    echo "Nodes $num_hosts" > "$outfile"
+    echo "Connections $num_flows" >> "$outfile"
+    for i in $(seq 0 $((num_flows - 1))); do
+        local src=$(( (i * step) % num_hosts ))
+        local dst=$(( (src + num_hosts / 2 + i * 7) % num_hosts ))
+        # Ensure src != dst
+        [ "$src" -eq "$dst" ] && dst=$(( (dst + 1) % num_hosts ))
+        echo "$src->$dst start 0 size 1048576" >> "$outfile"
+    done
+}
+
+# ============================================================
+# Test runner
+# ============================================================
+run_test() {
+    local label="$1"
+    local binary="$2"
+    local topo_path="$3"
+    local routing="$4"
+    local tm_file="$5"
+    local num_hosts="$6"
+    local workload_type="$7"   # "small" or "medium"
+    local num_flows="$8"
+    local topology="${9:-}"    # optional: dragonfly, slimfly
+    
+    TOTAL=$((TOTAL + 1))
+    local outfile="$TEST_DIR/out_${label}.txt"
+    
+    echo -n "  [$TOTAL] $label ... "
+    
+    # Build command
+    local cmd
+    if [ -n "$topology" ]; then
+        cmd="$binary -topology $topology -topo $topo_path -routing $routing -tm $tm_file"
+    else
+        cmd="$binary -topo $topo_path -routing $routing -tm $tm_file"
+    fi
+    
+    # Run with timeout (60s should be plenty for these workloads)
+    if timeout 60 $cmd > "$outfile" 2>&1; then
+        local exit_code=0
+    else
+        local exit_code=$?
+    fi
+    
+    # === Check 1: Did it complete? ===
+    if [ $exit_code -ne 0 ]; then
+        echo "FAIL (exit code $exit_code)"
+        FAIL=$((FAIL + 1))
+        cat "$outfile" | tail -5
+        return
+    fi
+    
+    if ! grep -q "Done" "$outfile"; then
+        echo "FAIL (no 'Done' in output)"
+        FAIL=$((FAIL + 1))
+        cat "$outfile" | tail -5
+        return
+    fi
+    
+    # === Check 2: Parse packet stats ===
+    local stats_line
+    stats_line=$(grep "^New:" "$outfile" || grep "New:" "$outfile" || true)
+    if [ -z "$stats_line" ]; then
+        echo "FAIL (no stats line)"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    
+    local new_pkts rtx_pkts ack_pkts nack_pkts bounced_pkts
+    new_pkts=$(echo "$stats_line" | grep -oP 'New: \K[0-9]+')
+    rtx_pkts=$(echo "$stats_line" | grep -oP 'Rtx: \K[0-9]+')
+    ack_pkts=$(echo "$stats_line" | grep -oP 'ACKs: \K[0-9]+')
+    nack_pkts=$(echo "$stats_line" | grep -oP 'NACKs: \K[0-9]+')
+    bounced_pkts=$(echo "$stats_line" | grep -oP 'Bounced: \K[0-9]+')
+    
+    # === Check 3: All flows completed (New packets > 0, ACKs received) ===
+    if [ "$new_pkts" -eq 0 ]; then
+        echo "FAIL (0 new packets sent)"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    
+    if [ "$ack_pkts" -eq 0 ]; then
+        echo "FAIL (0 ACKs received - flows didn't complete)"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    
+    # === Check 4: Expected packet count ===
+    # 1 MiB = 1048576 bytes, packet_size = 4160, data ≈ 4096 bytes 
+    # So ~256 packets per flow (1048576/4096). With 4160B packets, ~252.
+    # Allow range 240-270 per flow to account for protocol specifics.
+    local expected_min=$((num_flows * 240))
+    local expected_max=$((num_flows * 280))
+    
+    local pkt_check="OK"
+    if [ "$new_pkts" -lt "$expected_min" ] || [ "$new_pkts" -gt "$expected_max" ]; then
+        pkt_check="WARN(expected ${expected_min}-${expected_max})"
+    fi
+    
+    # === Check 5: Retransmission check ===
+    local rtx_check="OK"
+    if [ "$workload_type" = "small" ] && [ "$rtx_pkts" -gt 5 ]; then
+        # Single flow with no contention should have minimal retransmits
+        rtx_check="WARN(${rtx_pkts}rtx for single flow)"
+    fi
+    
+    # === Check 6: Recovery check - if there were NACKs/bounces, Rtx should be > 0 ===
+    local recovery_check="OK"
+    if [ "$nack_pkts" -gt 0 ] || [ "$bounced_pkts" -gt 0 ]; then
+        if [ "$rtx_pkts" -gt 0 ]; then
+            recovery_check="OK(recovered: ${rtx_pkts}rtx for ${nack_pkts}nack+${bounced_pkts}bounce)"
+        else
+            recovery_check="WARN(losses but 0 rtx)"
+        fi
+    fi
+    
+    echo "PASS | New:$new_pkts Rtx:$rtx_pkts ACK:$ack_pkts NACK:$nack_pkts Bounce:$bounced_pkts | pkt:$pkt_check rtx:$rtx_check recovery:$recovery_check"
+    PASS=$((PASS + 1))
+}
+
+# ============================================================
+# Generate all traffic matrices
+# ============================================================
+echo "=== Generating traffic matrices ==="
+
+# Dragonfly p3a6h3: 342 hosts, p=3
+make_single_flow_tm 342 "$TEST_DIR/df_p3a6h3_1flow.tm"
+make_medium_tm      342 "$TEST_DIR/df_p3a6h3_10flow.tm" 3
+
+# Dragonfly p4a8h4: 1056 hosts, p=4
+make_single_flow_tm 1056 "$TEST_DIR/df_p4a8h4_1flow.tm"
+make_medium_tm      1056 "$TEST_DIR/df_p4a8h4_10flow.tm" 4
+
+# Slimfly p4q5: 200 hosts, p=4
+make_single_flow_tm 200 "$TEST_DIR/sf_p4q5_1flow.tm"
+make_medium_tm      200 "$TEST_DIR/sf_p4q5_10flow.tm" 4
+
+echo "Done generating TMs"
+echo ""
+
+# ============================================================
+# Dragonfly p3a6h3 tests (342 hosts, has host_table → SOURCE works)
+# ============================================================
+echo "=== Dragonfly p3a6h3 (342 hosts) ==="
+DF_P3_PATH="$TOPO_DIR/dragonfly/p3a6h3"
+
+for routing in MINIMAL VALIANT UGAL_L SOURCE; do
+    run_test "df_p3a6h3_${routing}_1flow" "$UEC_BIN" "$DF_P3_PATH" "$routing" \
+        "$TEST_DIR/df_p3a6h3_1flow.tm" 342 "small" 1 "dragonfly"
+done
+echo ""
+echo "  -- Medium workload (10 flows) --"
+for routing in MINIMAL VALIANT UGAL_L SOURCE; do
+    run_test "df_p3a6h3_${routing}_10flow" "$UEC_BIN" "$DF_P3_PATH" "$routing" \
+        "$TEST_DIR/df_p3a6h3_10flow.tm" 342 "medium" 10 "dragonfly"
+done
+echo ""
+
+# ============================================================
+# Dragonfly p4a8h4 tests (1056 hosts, NO host_table → skip SOURCE)
+# ============================================================
+echo "=== Dragonfly p4a8h4 (1056 hosts) ==="
+DF_P4_PATH="$TOPO_DIR/dragonfly/p4a8h4"
+
+for routing in MINIMAL VALIANT UGAL_L; do
+    run_test "df_p4a8h4_${routing}_1flow" "$UEC_BIN" "$DF_P4_PATH" "$routing" \
+        "$TEST_DIR/df_p4a8h4_1flow.tm" 1056 "small" 1 "dragonfly"
+done
+echo ""
+echo "  -- Medium workload (10 flows) --"
+for routing in MINIMAL VALIANT UGAL_L; do
+    run_test "df_p4a8h4_${routing}_10flow" "$UEC_BIN" "$DF_P4_PATH" "$routing" \
+        "$TEST_DIR/df_p4a8h4_10flow.tm" 1056 "medium" 10 "dragonfly"
+done
+echo ""
+
+# ============================================================
+# Slimfly p4q5 tests (200 hosts, has host_table → SOURCE works)
+# ============================================================
+echo "=== Slimfly p4q5 (200 hosts) ==="
+SF_P4_PATH="$TOPO_DIR/slimfly/p4q5"
+
+for routing in MINIMAL VALIANT UGAL_L SOURCE; do
+    run_test "sf_p4q5_${routing}_1flow" "$UEC_BIN" "$SF_P4_PATH" "$routing" \
+        "$TEST_DIR/sf_p4q5_1flow.tm" 200 "small" 1 "slimfly"
+done
+echo ""
+echo "  -- Medium workload (10 flows) --"
+for routing in MINIMAL VALIANT UGAL_L SOURCE; do
+    run_test "sf_p4q5_${routing}_10flow" "$UEC_BIN" "$SF_P4_PATH" "$routing" \
+        "$TEST_DIR/sf_p4q5_10flow.tm" 200 "medium" 10 "slimfly"
+done
+echo ""
+
+# ============================================================
+# Summary
+# ============================================================
+echo "========================================="
+echo "  RESULTS: $PASS passed / $FAIL failed / $TOTAL total"
+echo "========================================="
+
+if [ $FAIL -gt 0 ]; then
+    echo "SOME TESTS FAILED"
+    exit 1
+else
+    echo "ALL TESTS PASSED"
+    exit 0
+fi
diff --git a/tests/run_e2e_tests.sh b/tests/run_e2e_tests.sh
new file mode 100755
index 0000000..2651da0
--- /dev/null
+++ b/tests/run_e2e_tests.sh
@@ -0,0 +1,415 @@
+#!/usr/bin/env bash
+# End-to-end stress & integration tests for the unified htsim_uec binary
+# Covers: larger topologies, heavy workloads, all routing combos, all-to-all,
+#         FT 1024 nodes, SF p7q9 (1134 hosts), bisection traffic, mixed sizes
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
+HTSIM_DIR="$REPO_DIR"
+UEC_BIN="$HTSIM_DIR/htsim/sim/datacenter/htsim_uec"
+TOPO_DIR="$HTSIM_DIR/htsim/sim/datacenter/topologies"
+TEST_DIR="$SCRIPT_DIR"
+TM_DIR="$TEST_DIR/e2e_tms"
+OUT_DIR="$TEST_DIR/e2e_out"
+
+mkdir -p "$TM_DIR" "$OUT_DIR"
+
+PASS=0
+FAIL=0
+TOTAL=0
+
+# ============================================================
+# Helper
+# ============================================================
+run_e2e_test() {
+    local label="$1"
+    local cmd="$2"
+    local expected_flows="$3"  # 0 = just check basic completion
+    local timeout_sec="${4:-120}"
+
+    TOTAL=$((TOTAL + 1))
+    local outfile="$OUT_DIR/out_${label}.txt"
+    echo -n "  [$TOTAL] $label ... "
+
+    if timeout "$timeout_sec" bash -c "$cmd" > "$outfile" 2>&1; then
+        local exit_code=0
+    else
+        local exit_code=$?
+    fi
+
+    if [ $exit_code -ne 0 ]; then
+        if [ $exit_code -eq 124 ]; then
+            echo "FAIL (timeout after ${timeout_sec}s)"
+        else
+            echo "FAIL (exit $exit_code)"
+            tail -5 "$outfile"
+        fi
+        FAIL=$((FAIL + 1)); return
+    fi
+
+    if ! grep -q "Done" "$outfile"; then
+        echo "FAIL (no 'Done')"
+        tail -5 "$outfile"
+        FAIL=$((FAIL + 1)); return
+    fi
+
+    local stats_line new_pkts ack_pkts rtx_pkts nack_pkts bounced_pkts
+    stats_line=$(grep "^New:" "$outfile" || grep "New:" "$outfile" | tail -1 || true)
+    if [ -z "$stats_line" ]; then
+        echo "FAIL (no stats)"
+        FAIL=$((FAIL + 1)); return
+    fi
+    new_pkts=$(echo "$stats_line" | grep -oP 'New: \K[0-9]+')
+    ack_pkts=$(echo "$stats_line" | grep -oP 'ACKs: \K[0-9]+')
+    rtx_pkts=$(echo "$stats_line" | grep -oP 'Rtx: \K[0-9]+' || echo 0)
+    nack_pkts=$(echo "$stats_line" | grep -oP 'NACKs: \K[0-9]+' || echo 0)
+    bounced_pkts=$(echo "$stats_line" | grep -oP 'Bounced: \K[0-9]+' || echo 0)
+
+    if [ "$new_pkts" -eq 0 ] || [ "$ack_pkts" -eq 0 ]; then
+        echo "FAIL (New=$new_pkts ACK=$ack_pkts)"
+        FAIL=$((FAIL + 1)); return
+    fi
+
+    if [ "$expected_flows" -gt 0 ]; then
+        local finished
+        finished=$(grep -c "finished at" "$outfile" || echo 0)
+        if [ "$finished" -ne "$expected_flows" ]; then
+            echo "FAIL (finished $finished of $expected_flows flows)"
+            FAIL=$((FAIL + 1)); return
+        fi
+    fi
+
+    echo "PASS | New:$new_pkts Rtx:$rtx_pkts ACK:$ack_pkts NACK:$nack_pkts Bounce:$bounced_pkts"
+    PASS=$((PASS + 1))
+}
+
+# ============================================================
+# TM generators
+# ============================================================
+make_bisection_tm() {
+    local num_hosts=$1 outfile=$2
+    local half=$((num_hosts / 2))
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $half"
+        for i in $(seq 0 $((half - 1))); do
+            echo "$i->$((i + half)) start 0 size 1048576"
+        done
+    } > "$outfile"
+}
+
+make_all_to_all_tm() {
+    local num_hosts=$1 outfile=$2 max_flows=${3:-0}
+    local count=0
+    local lines=""
+    for src in $(seq 0 $((num_hosts - 1))); do
+        for dst in $(seq 0 $((num_hosts - 1))); do
+            if [ "$src" -ne "$dst" ]; then
+                lines+="$src->$dst start 0 size 4096"$'\n'
+                count=$((count + 1))
+                if [ "$max_flows" -gt 0 ] && [ "$count" -ge "$max_flows" ]; then
+                    break 2
+                fi
+            fi
+        done
+    done
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $count"
+        printf "%s" "$lines"
+    } > "$outfile"
+}
+
+make_random_permutation_tm() {
+    local num_hosts=$1 outfile=$2 flow_size=${3:-1048576}
+    # Each host sends to (host + num_hosts/2) % num_hosts — a simple permutation
+    local half=$((num_hosts / 2))
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $num_hosts"
+        for src in $(seq 0 $((num_hosts - 1))); do
+            local dst=$(( (src + half) % num_hosts ))
+            echo "$src->$dst start 0 size $flow_size"
+        done
+    } > "$outfile"
+}
+
+make_heavy_incast_tm() {
+    local num_hosts=$1 outfile=$2 num_senders=$3 target=$4
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $num_senders"
+        for src in $(seq 0 $((num_senders - 1))); do
+            local s=$src
+            [ "$s" -eq "$target" ] && s=$((num_hosts - 1))
+            echo "$s->$target start 0 size 1048576"
+        done
+    } > "$outfile"
+}
+
+make_mixed_size_tm() {
+    local num_hosts=$1 outfile=$2
+    # Flows with varying sizes: 4KB, 64KB, 256KB, 1MB, 4MB
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections 5"
+        echo "0->$((num_hosts/5)) start 0 size 4096"
+        echo "$((num_hosts/5))->$((2*num_hosts/5)) start 0 size 65536"
+        echo "$((2*num_hosts/5))->$((3*num_hosts/5)) start 0 size 262144"
+        echo "$((3*num_hosts/5))->$((4*num_hosts/5)) start 0 size 1048576"
+        echo "1->$((num_hosts-1)) start 0 size 4194304"
+    } > "$outfile"
+}
+
+# ============================================================
+# Generate TMs
+# ============================================================
+echo "=== Generating E2E traffic matrices ==="
+
+# --- Fat Tree 128 ---
+make_bisection_tm 128 "$TM_DIR/ft128_bisection.tm"
+make_random_permutation_tm 128 "$TM_DIR/ft128_permutation.tm"
+make_heavy_incast_tm 128 "$TM_DIR/ft128_incast32.tm" 32 64
+make_mixed_size_tm 128 "$TM_DIR/ft128_mixed.tm"
+
+# --- Fat Tree 1024 ---
+cat > "$TM_DIR/ft1024_1flow.tm" <<'EOF'
+Nodes 1024
+Connections 1
+0->1023 start 0 size 1048576
+EOF
+
+cat > "$TM_DIR/ft1024_20flow.tm" <<EOF
+Nodes 1024
+Connections 20
+$(for i in $(seq 0 19); do echo "$((i*50))->$((1023 - i*50)) start 0 size 1048576"; done)
+EOF
+
+make_heavy_incast_tm 1024 "$TM_DIR/ft1024_incast32.tm" 32 512
+make_mixed_size_tm 1024 "$TM_DIR/ft1024_mixed.tm"
+
+# --- Dragonfly p3a6h3 (342 hosts) ---
+make_bisection_tm 342 "$TM_DIR/df342_bisection.tm"
+make_random_permutation_tm 342 "$TM_DIR/df342_permutation.tm"
+make_heavy_incast_tm 342 "$TM_DIR/df342_incast16.tm" 16 170
+make_mixed_size_tm 342 "$TM_DIR/df342_mixed.tm"
+
+# --- Dragonfly p4a8h4 (1056 hosts) ---
+cat > "$TM_DIR/df1056_20flow.tm" <<EOF
+Nodes 1056
+Connections 20
+$(for i in $(seq 0 19); do echo "$((i*50))->$((1055 - i*50)) start 0 size 1048576"; done)
+EOF
+make_heavy_incast_tm 1056 "$TM_DIR/df1056_incast16.tm" 16 528
+make_mixed_size_tm 1056 "$TM_DIR/df1056_mixed.tm"
+
+# --- Slimfly p4q5 (200 hosts) ---
+make_bisection_tm 200 "$TM_DIR/sf200_bisection.tm"
+make_random_permutation_tm 200 "$TM_DIR/sf200_permutation.tm"
+make_heavy_incast_tm 200 "$TM_DIR/sf200_incast16.tm" 16 100
+make_mixed_size_tm 200 "$TM_DIR/sf200_mixed.tm"
+
+# --- Slimfly p7q9 (1134 hosts) ---
+cat > "$TM_DIR/sf1134_1flow.tm" <<'EOF'
+Nodes 1134
+Connections 1
+0->1133 start 0 size 1048576
+EOF
+
+cat > "$TM_DIR/sf1134_20flow.tm" <<EOF
+Nodes 1134
+Connections 20
+$(for i in $(seq 0 19); do echo "$((i*50))->$((1133 - i*50)) start 0 size 1048576"; done)
+EOF
+make_heavy_incast_tm 1134 "$TM_DIR/sf1134_incast16.tm" 16 567
+make_mixed_size_tm 1134 "$TM_DIR/sf1134_mixed.tm"
+
+echo "Done generating E2E TMs"
+echo ""
+
+FT128="$TOPO_DIR/fat_tree_128_1os.topo"
+FT1024="$TOPO_DIR/fat_tree_1024_1os.topo"
+DF_P3="$TOPO_DIR/dragonfly/p3a6h3"
+DF_P4="$TOPO_DIR/dragonfly/p4a8h4"
+SF_P4="$TOPO_DIR/slimfly/p4q5"
+SF_P7="$TOPO_DIR/slimfly/p7q9"
+
+# ============================================================
+# Section 1: Fat Tree E2E
+# ============================================================
+echo "=== Section 1: Fat Tree 128 — E2E patterns ==="
+
+run_e2e_test "ft128_bisection_64flows" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_bisection.tm -cwnd 30 -q 88" \
+    64
+
+run_e2e_test "ft128_permutation_128flows" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_permutation.tm -cwnd 30 -q 88" \
+    128
+
+run_e2e_test "ft128_incast_32to1" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_incast32.tm -cwnd 30 -q 88" \
+    32
+
+run_e2e_test "ft128_mixed_sizes" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_mixed.tm -cwnd 30 -q 88" \
+    5
+
+echo ""
+echo "=== Section 2: Fat Tree 1024 — larger scale ==="
+
+run_e2e_test "ft1024_1flow" \
+    "$UEC_BIN -topo $FT1024 -tm $TM_DIR/ft1024_1flow.tm -cwnd 30 -q 88" \
+    1 180
+
+run_e2e_test "ft1024_20flows" \
+    "$UEC_BIN -topo $FT1024 -tm $TM_DIR/ft1024_20flow.tm -cwnd 30 -q 88" \
+    20 180
+
+run_e2e_test "ft1024_incast_32to1" \
+    "$UEC_BIN -topo $FT1024 -tm $TM_DIR/ft1024_incast32.tm -cwnd 30 -q 88" \
+    32 180
+
+run_e2e_test "ft1024_mixed_sizes" \
+    "$UEC_BIN -topo $FT1024 -tm $TM_DIR/ft1024_mixed.tm -cwnd 30 -q 88" \
+    5 180
+
+echo ""
+
+# ============================================================
+# Section 3: Dragonfly E2E
+# ============================================================
+echo "=== Section 3: Dragonfly p3a6h3 (342 hosts) — E2E patterns ==="
+
+run_e2e_test "df342_bisection_MINIMAL" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_bisection.tm -routing MINIMAL -q 88" \
+    171
+
+run_e2e_test "df342_bisection_VALIANT" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_bisection.tm -routing VALIANT -q 88" \
+    171
+
+run_e2e_test "df342_permutation_MINIMAL" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_permutation.tm -routing MINIMAL -q 88" \
+    342
+
+run_e2e_test "df342_permutation_UGAL_L" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_permutation.tm -routing UGAL_L -q 88" \
+    342
+
+run_e2e_test "df342_incast_16_MINIMAL" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_incast16.tm -routing MINIMAL -q 88" \
+    16
+
+run_e2e_test "df342_mixed_SOURCE" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_mixed.tm -routing SOURCE -q 88" \
+    5
+
+echo ""
+echo "=== Section 4: Dragonfly p4a8h4 (1056 hosts) — larger scale ==="
+
+run_e2e_test "df1056_20flows_MINIMAL" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P4 -tm $TM_DIR/df1056_20flow.tm -routing MINIMAL -q 88" \
+    20 180
+
+run_e2e_test "df1056_20flows_VALIANT" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P4 -tm $TM_DIR/df1056_20flow.tm -routing VALIANT -q 88" \
+    20 180
+
+run_e2e_test "df1056_incast_16_UGAL_L" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P4 -tm $TM_DIR/df1056_incast16.tm -routing UGAL_L -q 88" \
+    16 180
+
+run_e2e_test "df1056_mixed_MINIMAL" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P4 -tm $TM_DIR/df1056_mixed.tm -routing MINIMAL -q 88" \
+    5 180
+
+echo ""
+
+# ============================================================
+# Section 5: SlimFly E2E
+# ============================================================
+echo "=== Section 5: Slimfly p4q5 (200 hosts) — E2E patterns ==="
+
+run_e2e_test "sf200_bisection_MINIMAL" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_bisection.tm -routing MINIMAL -q 88" \
+    100
+
+run_e2e_test "sf200_bisection_VALIANT" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_bisection.tm -routing VALIANT -q 88" \
+    100
+
+run_e2e_test "sf200_permutation_MINIMAL" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_permutation.tm -routing MINIMAL -q 88" \
+    200
+
+run_e2e_test "sf200_permutation_SOURCE" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_permutation.tm -routing SOURCE -q 88" \
+    200
+
+run_e2e_test "sf200_incast_16_MINIMAL" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_incast16.tm -routing MINIMAL -q 88" \
+    16
+
+run_e2e_test "sf200_mixed_UGAL_L" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_mixed.tm -routing UGAL_L -q 88" \
+    5
+
+echo ""
+echo "=== Section 6: Slimfly p7q9 (1134 hosts) — larger scale ==="
+
+run_e2e_test "sf1134_1flow_MINIMAL" \
+    "$UEC_BIN -topology slimfly -topo $SF_P7 -tm $TM_DIR/sf1134_1flow.tm -routing MINIMAL -q 88" \
+    1 180
+
+run_e2e_test "sf1134_20flows_MINIMAL" \
+    "$UEC_BIN -topology slimfly -topo $SF_P7 -tm $TM_DIR/sf1134_20flow.tm -routing MINIMAL -q 88" \
+    20 180
+
+run_e2e_test "sf1134_20flows_SOURCE" \
+    "$UEC_BIN -topology slimfly -topo $SF_P7 -tm $TM_DIR/sf1134_20flow.tm -routing SOURCE -q 88" \
+    20 180
+
+run_e2e_test "sf1134_incast_16_MINIMAL" \
+    "$UEC_BIN -topology slimfly -topo $SF_P7 -tm $TM_DIR/sf1134_incast16.tm -routing MINIMAL -q 88" \
+    16 180
+
+run_e2e_test "sf1134_mixed_MINIMAL" \
+    "$UEC_BIN -topology slimfly -topo $SF_P7 -tm $TM_DIR/sf1134_mixed.tm -routing MINIMAL -q 88" \
+    5 180
+
+echo ""
+
+# ============================================================
+# Section 7: All routing algorithms × all topologies (single flow)
+# ============================================================
+echo "=== Section 7: Routing algorithm matrix (1 flow each) ==="
+
+for routing in MINIMAL VALIANT UGAL_L SOURCE; do
+    run_e2e_test "matrix_df342_${routing}" \
+        "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_mixed.tm -routing $routing -q 88" \
+        5
+done
+
+for routing in MINIMAL VALIANT UGAL_L SOURCE; do
+    run_e2e_test "matrix_sf200_${routing}" \
+        "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_mixed.tm -routing $routing -q 88" \
+        5
+done
+
+echo ""
+
+# ============================================================
+# Summary
+# ============================================================
+echo "========================================="
+echo "  E2E RESULTS: $PASS passed / $FAIL failed / $TOTAL total"
+echo "========================================="
+if [ $FAIL -gt 0 ]; then
+    echo "SOME TESTS FAILED"
+    exit 1
+else
+    echo "ALL E2E TESTS PASSED"
+    exit 0
+fi
diff --git a/tests/run_edge_case_tests.sh b/tests/run_edge_case_tests.sh
new file mode 100755
index 0000000..8f82578
--- /dev/null
+++ b/tests/run_edge_case_tests.sh
@@ -0,0 +1,474 @@
+#!/usr/bin/env bash
+# Edge case & parameter variation tests for the unified htsim_uec binary
+# Covers: default topology, explicit FT flag, cwnd variations, queue sizes,
+#         tiny/large flows, staggered starts, single-packet flows, incast
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
+HTSIM_DIR="$REPO_DIR"
+UEC_BIN="$HTSIM_DIR/htsim/sim/datacenter/htsim_uec"
+TOPO_DIR="$HTSIM_DIR/htsim/sim/datacenter/topologies"
+TEST_DIR="$SCRIPT_DIR"
+TM_DIR="$TEST_DIR/edge_tms"
+OUT_DIR="$TEST_DIR/edge_out"
+
+mkdir -p "$TM_DIR" "$OUT_DIR"
+
+PASS=0
+FAIL=0
+TOTAL=0
+
+# ============================================================
+# Helpers
+# ============================================================
+run_edge_test() {
+    local label="$1"
+    local cmd="$2"
+    local check_type="$3"  # "basic" | "flow_count:N" | "no_crash"
+
+    TOTAL=$((TOTAL + 1))
+    local outfile="$OUT_DIR/out_${label}.txt"
+    echo -n "  [$TOTAL] $label ... "
+
+    if timeout 90 bash -c "$cmd" > "$outfile" 2>&1; then
+        local exit_code=0
+    else
+        local exit_code=$?
+    fi
+
+    # --- no_crash: only checks it doesn't segfault ---
+    if [ "$check_type" = "no_crash" ]; then
+        if [ $exit_code -eq 139 ] || [ $exit_code -eq 136 ]; then
+            echo "FAIL (segfault/FPE, exit $exit_code)"
+            FAIL=$((FAIL + 1)); return
+        fi
+        echo "PASS (exit $exit_code)"
+        PASS=$((PASS + 1)); return
+    fi
+
+    # --- expected_abort: expect assertion failure (exit 134) or nonzero exit ---
+    if [ "$check_type" = "expected_abort" ]; then
+        if [ $exit_code -ne 0 ]; then
+            echo "PASS (correctly aborted, exit $exit_code)"
+            PASS=$((PASS + 1)); return
+        fi
+        echo "FAIL (expected abort but got exit 0)"
+        FAIL=$((FAIL + 1)); return
+    fi
+
+    # --- basic / flow_count: must complete ---
+    if [ $exit_code -ne 0 ]; then
+        echo "FAIL (exit code $exit_code)"
+        tail -5 "$outfile"
+        FAIL=$((FAIL + 1)); return
+    fi
+
+    if ! grep -q "Done" "$outfile"; then
+        echo "FAIL (no 'Done')"
+        tail -5 "$outfile"
+        FAIL=$((FAIL + 1)); return
+    fi
+
+    local stats_line new_pkts ack_pkts
+    stats_line=$(grep "^New:" "$outfile" || grep "New:" "$outfile" | tail -1 || true)
+    if [ -z "$stats_line" ]; then
+        echo "FAIL (no stats)"
+        FAIL=$((FAIL + 1)); return
+    fi
+    new_pkts=$(echo "$stats_line" | grep -oP 'New: \K[0-9]+')
+    ack_pkts=$(echo "$stats_line" | grep -oP 'ACKs: \K[0-9]+')
+
+    if [ "$new_pkts" -eq 0 ] || [ "$ack_pkts" -eq 0 ]; then
+        echo "FAIL (New=$new_pkts, ACK=$ack_pkts)"
+        FAIL=$((FAIL + 1)); return
+    fi
+
+    # --- flow_count check ---
+    if [[ "$check_type" == flow_count:* ]]; then
+        local expected=${check_type#flow_count:}
+        local finished
+        finished=$(grep -c "finished at" "$outfile" || echo 0)
+        if [ "$finished" -ne "$expected" ]; then
+            echo "FAIL (finished $finished of $expected flows)"
+            FAIL=$((FAIL + 1)); return
+        fi
+    fi
+
+    local rtx_pkts nack_pkts bounced_pkts
+    rtx_pkts=$(echo "$stats_line" | grep -oP 'Rtx: \K[0-9]+' || echo 0)
+    nack_pkts=$(echo "$stats_line" | grep -oP 'NACKs: \K[0-9]+' || echo 0)
+    bounced_pkts=$(echo "$stats_line" | grep -oP 'Bounced: \K[0-9]+' || echo 0)
+    echo "PASS | New:$new_pkts Rtx:$rtx_pkts ACK:$ack_pkts NACK:$nack_pkts Bounce:$bounced_pkts"
+    PASS=$((PASS + 1))
+}
+
+# ============================================================
+# Generate traffic matrices
+# ============================================================
+echo "=== Generating edge-case traffic matrices ==="
+
+# --- Fat Tree 128 nodes ---
+cat > "$TM_DIR/ft128_1flow.tm" <<'EOF'
+Nodes 128
+Connections 1
+0->127 start 0 size 1048576
+EOF
+
+cat > "$TM_DIR/ft128_5flow.tm" <<'EOF'
+Nodes 128
+Connections 5
+0->127 start 0 size 1048576
+1->126 start 0 size 1048576
+10->100 start 0 size 1048576
+30->90 start 0 size 1048576
+64->63 start 0 size 1048576
+EOF
+
+# Tiny flow: 1 packet (4096 bytes)
+cat > "$TM_DIR/ft128_tiny.tm" <<'EOF'
+Nodes 128
+Connections 1
+0->127 start 0 size 4096
+EOF
+
+# Large flow: 10 MiB
+cat > "$TM_DIR/ft128_large.tm" <<'EOF'
+Nodes 128
+Connections 1
+0->127 start 0 size 10485760
+EOF
+
+# Staggered starts (different start times in ns)
+cat > "$TM_DIR/ft128_staggered.tm" <<'EOF'
+Nodes 128
+Connections 4
+0->64 start 0 size 1048576
+1->65 start 1000 size 1048576
+2->66 start 5000 size 1048576
+3->67 start 10000 size 1048576
+EOF
+
+# Incast: many sources → one destination
+cat > "$TM_DIR/ft128_incast_16to1.tm" <<'EOF'
+Nodes 128
+Connections 16
+0->127 start 0 size 1048576
+1->127 start 0 size 1048576
+2->127 start 0 size 1048576
+3->127 start 0 size 1048576
+4->127 start 0 size 1048576
+5->127 start 0 size 1048576
+6->127 start 0 size 1048576
+7->127 start 0 size 1048576
+8->127 start 0 size 1048576
+9->127 start 0 size 1048576
+10->127 start 0 size 1048576
+11->127 start 0 size 1048576
+12->127 start 0 size 1048576
+13->127 start 0 size 1048576
+14->127 start 0 size 1048576
+15->127 start 0 size 1048576
+EOF
+
+# Outcast: one source → many destinations
+cat > "$TM_DIR/ft128_outcast_1to16.tm" <<'EOF'
+Nodes 128
+Connections 16
+0->8 start 0 size 1048576
+0->16 start 0 size 1048576
+0->24 start 0 size 1048576
+0->32 start 0 size 1048576
+0->40 start 0 size 1048576
+0->48 start 0 size 1048576
+0->56 start 0 size 1048576
+0->64 start 0 size 1048576
+0->72 start 0 size 1048576
+0->80 start 0 size 1048576
+0->88 start 0 size 1048576
+0->96 start 0 size 1048576
+0->104 start 0 size 1048576
+0->112 start 0 size 1048576
+0->120 start 0 size 1048576
+0->127 start 0 size 1048576
+EOF
+
+# Same-pod traffic (nodes 0-15 are in the same pod for 128-node FT with podsize 16)
+cat > "$TM_DIR/ft128_samepod.tm" <<'EOF'
+Nodes 128
+Connections 4
+0->15 start 0 size 1048576
+1->14 start 0 size 1048576
+2->13 start 0 size 1048576
+3->12 start 0 size 1048576
+EOF
+
+# Cross-pod traffic (nodes in different pods)
+cat > "$TM_DIR/ft128_crosspod.tm" <<'EOF'
+Nodes 128
+Connections 4
+0->16 start 0 size 1048576
+1->32 start 0 size 1048576
+2->48 start 0 size 1048576
+3->64 start 0 size 1048576
+EOF
+
+# --- Dragonfly p3a6h3 (342 hosts) edge TMs ---
+cat > "$TM_DIR/df342_tiny.tm" <<'EOF'
+Nodes 342
+Connections 1
+0->341 start 0 size 4096
+EOF
+
+cat > "$TM_DIR/df342_large.tm" <<'EOF'
+Nodes 342
+Connections 1
+0->200 start 0 size 10485760
+EOF
+
+cat > "$TM_DIR/df342_staggered.tm" <<'EOF'
+Nodes 342
+Connections 4
+0->100 start 0 size 1048576
+50->200 start 2000 size 1048576
+100->300 start 5000 size 1048576
+150->341 start 10000 size 1048576
+EOF
+
+cat > "$TM_DIR/df342_incast_8to1.tm" <<EOF
+Nodes 342
+Connections 8
+$(for i in $(seq 0 7); do echo "$i->341 start 0 size 1048576"; done)
+EOF
+
+# --- Slimfly p4q5 (200 hosts) edge TMs ---
+cat > "$TM_DIR/sf200_tiny.tm" <<'EOF'
+Nodes 200
+Connections 1
+0->199 start 0 size 4096
+EOF
+
+cat > "$TM_DIR/sf200_large.tm" <<'EOF'
+Nodes 200
+Connections 1
+0->150 start 0 size 10485760
+EOF
+
+cat > "$TM_DIR/sf200_staggered.tm" <<'EOF'
+Nodes 200
+Connections 4
+0->50 start 0 size 1048576
+25->100 start 2000 size 1048576
+75->150 start 5000 size 1048576
+100->199 start 10000 size 1048576
+EOF
+
+cat > "$TM_DIR/sf200_incast_8to1.tm" <<EOF
+Nodes 200
+Connections 8
+$(for i in $(seq 0 7); do echo "$i->199 start 0 size 1048576"; done)
+EOF
+
+echo "Done generating edge-case TMs"
+echo ""
+
+# ============================================================
+# Section 1: Fat Tree — default topology (no -topology flag)
+# ============================================================
+FT128="$TOPO_DIR/fat_tree_128_1os.topo"
+
+echo "=== Section 1: Fat Tree basic (default topology type) ==="
+
+run_edge_test "ft_default_no_flag" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_1flow.tm -cwnd 30 -q 88" \
+    "basic"
+
+run_edge_test "ft_explicit_fattree_flag" \
+    "$UEC_BIN -topology fattree -topo $FT128 -tm $TM_DIR/ft128_1flow.tm -cwnd 30 -q 88" \
+    "basic"
+
+echo ""
+
+# ============================================================
+# Section 2: Fat Tree — parameter variations
+# ============================================================
+echo "=== Section 2: Fat Tree parameter variations ==="
+
+# Different cwnd values
+for cwnd in 5 15 30 50 100; do
+    run_edge_test "ft_cwnd_${cwnd}" \
+        "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_1flow.tm -cwnd $cwnd -q 88" \
+        "basic"
+done
+echo ""
+
+# Different queue sizes
+echo "  -- Queue size variations --"
+# qsize=20 is too small for ECN thresholds — expect assertion abort
+run_edge_test "ft_qsize_20_expected_abort" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_1flow.tm -cwnd 30 -q 20" \
+    "expected_abort"
+for qsize in 50 88 150 300; do
+    run_edge_test "ft_qsize_${qsize}" \
+        "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_1flow.tm -cwnd 30 -q $qsize" \
+        "basic"
+done
+echo ""
+
+# ============================================================
+# Section 3: Fat Tree — flow patterns
+# ============================================================
+echo "=== Section 3: Fat Tree flow patterns ==="
+
+run_edge_test "ft_tiny_flow" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_tiny.tm -cwnd 30 -q 88" \
+    "flow_count:1"
+
+run_edge_test "ft_large_flow_10MiB" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_large.tm -cwnd 30 -q 88" \
+    "basic"
+
+run_edge_test "ft_5flows" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_5flow.tm -cwnd 30 -q 88" \
+    "flow_count:5"
+
+run_edge_test "ft_staggered_starts" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_staggered.tm -cwnd 30 -q 88" \
+    "flow_count:4"
+
+run_edge_test "ft_incast_16to1" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_incast_16to1.tm -cwnd 30 -q 88" \
+    "flow_count:16"
+
+run_edge_test "ft_outcast_1to16" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_outcast_1to16.tm -cwnd 30 -q 88" \
+    "flow_count:16"
+
+run_edge_test "ft_samepod" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_samepod.tm -cwnd 30 -q 88" \
+    "flow_count:4"
+
+run_edge_test "ft_crosspod" \
+    "$UEC_BIN -topo $FT128 -tm $TM_DIR/ft128_crosspod.tm -cwnd 30 -q 88" \
+    "flow_count:4"
+
+echo ""
+
+# ============================================================
+# Section 4: Dragonfly — edge cases
+# ============================================================
+echo "=== Section 4: Dragonfly edge cases ==="
+DF_P3="$TOPO_DIR/dragonfly/p3a6h3"
+
+run_edge_test "df_tiny_flow" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_tiny.tm -routing MINIMAL -q 88" \
+    "flow_count:1"
+
+run_edge_test "df_large_flow_10MiB" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_large.tm -routing MINIMAL -q 88" \
+    "basic"
+
+run_edge_test "df_staggered_starts" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_staggered.tm -routing MINIMAL -q 88" \
+    "flow_count:4"
+
+run_edge_test "df_incast_8to1" \
+    "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_incast_8to1.tm -routing MINIMAL -q 88" \
+    "flow_count:8"
+
+# cwnd variations on DF (DF uses cwnd as raw bytes, not packet count)
+# Values must be large enough to fit at least 1 packet (~4160 bytes)
+for cwnd in 20000 100000 500000; do
+    run_edge_test "df_cwnd_${cwnd}" \
+        "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_tiny.tm -routing MINIMAL -q 88 -cwnd $cwnd" \
+        "basic"
+done
+
+# queue size variations on DF
+for qsize in 30 88 200; do
+    run_edge_test "df_qsize_${qsize}" \
+        "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_tiny.tm -routing MINIMAL -q $qsize" \
+        "basic"
+done
+
+echo ""
+
+# ============================================================
+# Section 5: SlimFly — edge cases
+# ============================================================
+echo "=== Section 5: SlimFly edge cases ==="
+SF_P4="$TOPO_DIR/slimfly/p4q5"
+
+run_edge_test "sf_tiny_flow" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_tiny.tm -routing MINIMAL -q 88" \
+    "flow_count:1"
+
+run_edge_test "sf_large_flow_10MiB" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_large.tm -routing MINIMAL -q 88" \
+    "basic"
+
+run_edge_test "sf_staggered_starts" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_staggered.tm -routing MINIMAL -q 88" \
+    "flow_count:4"
+
+run_edge_test "sf_incast_8to1" \
+    "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_incast_8to1.tm -routing MINIMAL -q 88" \
+    "flow_count:8"
+
+# cwnd variations on SF (SF uses cwnd as raw bytes, not packet count)
+# Values must be large enough to fit at least 1 packet (~4160 bytes)
+for cwnd in 20000 100000 500000; do
+    run_edge_test "sf_cwnd_${cwnd}" \
+        "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_tiny.tm -routing MINIMAL -q 88 -cwnd $cwnd" \
+        "basic"
+done
+
+# queue size variations on SF
+for qsize in 30 88 200; do
+    run_edge_test "sf_qsize_${qsize}" \
+        "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_tiny.tm -routing MINIMAL -q $qsize" \
+        "basic"
+done
+
+echo ""
+
+# ============================================================
+# Section 6: Cross-topology consistency
+# Same workload pattern on all 3 topologies should all complete
+# ============================================================
+echo "=== Section 6: Cross-topology consistency ==="
+
+# 1-flow, 1 MiB on each topology
+run_edge_test "consistency_ft_1flow" \
+    "$UEC_BIN -topology fattree -topo $FT128 -tm $TM_DIR/ft128_1flow.tm -cwnd 30 -q 88" \
+    "flow_count:1"
+
+# DF 1-flow with each routing algo
+for routing in MINIMAL VALIANT UGAL_L SOURCE; do
+    run_edge_test "consistency_df_${routing}" \
+        "$UEC_BIN -topology dragonfly -topo $DF_P3 -tm $TM_DIR/df342_tiny.tm -routing $routing -q 88" \
+        "flow_count:1"
+done
+
+# SF 1-flow with each routing algo
+for routing in MINIMAL VALIANT UGAL_L SOURCE; do
+    run_edge_test "consistency_sf_${routing}" \
+        "$UEC_BIN -topology slimfly -topo $SF_P4 -tm $TM_DIR/sf200_tiny.tm -routing $routing -q 88" \
+        "flow_count:1"
+done
+
+echo ""
+
+# ============================================================
+# Summary
+# ============================================================
+echo "========================================="
+echo "  EDGE CASE RESULTS: $PASS passed / $FAIL failed / $TOTAL total"
+echo "========================================="
+if [ $FAIL -gt 0 ]; then
+    echo "SOME TESTS FAILED"
+    exit 1
+else
+    echo "ALL EDGE CASE TESTS PASSED"
+    exit 0
+fi
diff --git a/tests/run_reachability_tests.sh b/tests/run_reachability_tests.sh
new file mode 100755
index 0000000..adc901d
--- /dev/null
+++ b/tests/run_reachability_tests.sh
@@ -0,0 +1,313 @@
+#!/usr/bin/env bash
+# Extended reachability & connectivity tests for HTSIM dragonfly and slimfly
+# Tests: one-to-all, all-to-one, same-switch, cross-group, edge cases
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+REPO_DIR="$(cd "$SCRIPT_DIR/.." && pwd)"
+HTSIM_DIR="$REPO_DIR"
+UEC_BIN="$HTSIM_DIR/htsim/sim/datacenter/htsim_uec"
+TOPO_DIR="$HTSIM_DIR/htsim/sim/datacenter/topologies"
+TEST_DIR="$SCRIPT_DIR"
+
+PASS=0
+FAIL=0
+TOTAL=0
+
+FLOW_SIZE=4096  # 1 packet — minimal for reachability check
+
+# ============================================================
+# TM generators
+# ============================================================
+
+# One-to-all: node 0 → every other node
+make_one_to_all_tm() {
+    local num_hosts=$1 outfile=$2
+    local n=$((num_hosts - 1))
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $n"
+        for dst in $(seq 1 $((num_hosts - 1))); do
+            echo "0->$dst start 0 size $FLOW_SIZE"
+        done
+    } > "$outfile"
+}
+
+# All-to-one: every node → node 0
+make_all_to_one_tm() {
+    local num_hosts=$1 outfile=$2
+    local n=$((num_hosts - 1))
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $n"
+        for src in $(seq 1 $((num_hosts - 1))); do
+            echo "$src->0 start 0 size $FLOW_SIZE"
+        done
+    } > "$outfile"
+}
+
+# Same-switch: flows between hosts on the same switch (intra-switch)
+make_same_switch_tm() {
+    local num_hosts=$1 p=$2 outfile=$3
+    local num_switches=$((num_hosts / p))
+    local count=0
+    local lines=""
+    # For each switch, first host → last host on that switch
+    for sw in $(seq 0 $((num_switches - 1))); do
+        local src=$((sw * p))
+        local dst=$((sw * p + p - 1))
+        if [ "$src" -ne "$dst" ]; then
+            lines+="$src->$dst start 0 size $FLOW_SIZE"$'\n'
+            count=$((count + 1))
+        fi
+    done
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $count"
+        printf "%s" "$lines"
+    } > "$outfile"
+}
+
+# Cross-group: for dragonfly, pick one host from each group → host in a different group
+# groups = a*h+1, each group has a switches, each switch has p hosts
+make_cross_group_tm() {
+    local num_hosts=$1 p=$2 a=$3 h=$4 outfile=$5
+    local num_groups=$(( a * h + 1 ))
+    local count=0
+    local lines=""
+    for g in $(seq 0 $((num_groups - 1))); do
+        local src=$((g * a * p))           # first host in group g
+        local dst_group=$(( (g + num_groups / 2) % num_groups ))
+        local dst=$((dst_group * a * p))   # first host in opposite group
+        if [ "$src" -ne "$dst" ] && [ "$src" -lt "$num_hosts" ] && [ "$dst" -lt "$num_hosts" ]; then
+            lines+="$src->$dst start 0 size $FLOW_SIZE"$'\n'
+            count=$((count + 1))
+        fi
+    done
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $count"
+        printf "%s" "$lines"
+    } > "$outfile"
+}
+
+# Cross-partition: for slimfly, pick hosts across the two partitions (switch 0..q²-1 and q²..2q²-1)
+make_cross_partition_tm() {
+    local num_hosts=$1 p=$2 q=$3 outfile=$4
+    local q2=$((q * q))
+    local count=0
+    local lines=""
+    # For each switch in partition 0, connect to corresponding switch in partition 1
+    for sw in $(seq 0 $((q2 - 1))); do
+        local src=$((sw * p))                     # first host on switch sw (partition 0)
+        local dst=$(( (q2 + sw) * p ))            # first host on switch q²+sw (partition 1)
+        if [ "$src" -lt "$num_hosts" ] && [ "$dst" -lt "$num_hosts" ]; then
+            lines+="$src->$dst start 0 size $FLOW_SIZE"$'\n'
+            count=$((count + 1))
+        fi
+    done
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $count"
+        printf "%s" "$lines"
+    } > "$outfile"
+}
+
+# Maximum-distance pairs: for dragonfly, hosts at group 0 ↔ last group
+make_max_distance_df_tm() {
+    local num_hosts=$1 p=$2 a=$3 h=$4 outfile=$5
+    local num_groups=$(( a * h + 1 ))
+    local last_group=$((num_groups - 1))
+    local count=0
+    local lines=""
+    # p flows from group 0 → last group
+    for i in $(seq 0 $((p - 1))); do
+        local src=$i
+        local dst=$((last_group * a * p + i))
+        if [ "$dst" -lt "$num_hosts" ]; then
+            lines+="$src->$dst start 0 size $FLOW_SIZE"$'\n'
+            count=$((count + 1))
+        fi
+    done
+    {
+        echo "Nodes $num_hosts"
+        echo "Connections $count"
+        printf "%s" "$lines"
+    } > "$outfile"
+}
+
+# ============================================================
+# Test runner
+# ============================================================
+run_reachability_test() {
+    local label="$1"
+    local binary="$2"
+    local topo_path="$3"
+    local routing="$4"
+    local tm_file="$5"
+    local expected_flows="$6"
+    local topology="${7:-}"    # optional: dragonfly, slimfly
+    
+    TOTAL=$((TOTAL + 1))
+    local outfile="$TEST_DIR/out_reach_${label}.txt"
+    
+    echo -n "  [$TOTAL] $label ($expected_flows flows) ... "
+    
+    # Build command
+    local cmd
+    if [ -n "$topology" ]; then
+        cmd="$binary -topology $topology -topo $topo_path -routing $routing -tm $tm_file"
+    else
+        cmd="$binary -topo $topo_path -routing $routing -tm $tm_file"
+    fi
+    
+    # Run with timeout
+    if timeout 120 $cmd > "$outfile" 2>&1; then
+        local exit_code=0
+    else
+        local exit_code=$?
+    fi
+    
+    # Check 1: exited cleanly
+    if [ $exit_code -ne 0 ]; then
+        echo "FAIL (exit code $exit_code)"
+        tail -3 "$outfile"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    
+    # Check 2: "Done" in output
+    if ! grep -q "Done" "$outfile"; then
+        echo "FAIL (no 'Done')"
+        tail -3 "$outfile"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    
+    # Check 3: count finished flows
+    local finished_count
+    finished_count=$(grep -c "finished at" "$outfile" || echo 0)
+    
+    if [ "$finished_count" -ne "$expected_flows" ]; then
+        echo "FAIL (only $finished_count of $expected_flows flows finished)"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    
+    # Check 4: all flows got correct bytes
+    local wrong_bytes
+    wrong_bytes=$(grep "finished at" "$outfile" | grep -cv "total bytes $FLOW_SIZE" || true)
+    if [ "$wrong_bytes" -gt 0 ]; then
+        echo "FAIL ($wrong_bytes flows got wrong byte count)"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    
+    # Check 5: New packets count (1 flow = 1 packet for 4096B)
+    local stats_line new_pkts
+    stats_line=$(grep "New:" "$outfile" | tail -1)
+    new_pkts=$(echo "$stats_line" | grep -oP 'New: \K[0-9]+')
+    
+    if [ "$new_pkts" -ne "$expected_flows" ]; then
+        echo "FAIL (New=$new_pkts, expected $expected_flows)"
+        FAIL=$((FAIL + 1))
+        return
+    fi
+    
+    local rtx_pkts ack_pkts
+    rtx_pkts=$(echo "$stats_line" | grep -oP 'Rtx: \K[0-9]+')
+    ack_pkts=$(echo "$stats_line" | grep -oP 'ACKs: \K[0-9]+')
+    
+    echo "PASS (all $finished_count flows finished, New=$new_pkts Rtx=$rtx_pkts ACK=$ack_pkts)"
+    PASS=$((PASS + 1))
+}
+
+# ============================================================
+# Generate TMs
+# ============================================================
+echo "=== Generating reachability traffic matrices ==="
+
+# --- Dragonfly p3a6h3: 342 hosts, p=3, a=6, h=3 ---
+make_one_to_all_tm   342 "$TEST_DIR/df_p3_one2all.tm"
+make_all_to_one_tm   342 "$TEST_DIR/df_p3_all2one.tm"
+make_same_switch_tm  342 3 "$TEST_DIR/df_p3_sameswitch.tm"
+make_cross_group_tm  342 3 6 3 "$TEST_DIR/df_p3_crossgroup.tm"
+make_max_distance_df_tm 342 3 6 3 "$TEST_DIR/df_p3_maxdist.tm"
+
+# --- Slimfly p4q5: 200 hosts, p=4, q=5 ---
+make_one_to_all_tm    200 "$TEST_DIR/sf_p4_one2all.tm"
+make_all_to_one_tm    200 "$TEST_DIR/sf_p4_all2one.tm"
+make_same_switch_tm   200 4 "$TEST_DIR/sf_p4_sameswitch.tm"
+make_cross_partition_tm 200 4 5 "$TEST_DIR/sf_p4_crosspart.tm"
+
+echo "Done"
+echo ""
+
+# ============================================================
+# Dragonfly p3a6h3 — MINIMAL & SOURCE routing
+# ============================================================
+DF_P3="$TOPO_DIR/dragonfly/p3a6h3"
+
+echo "=== Dragonfly p3a6h3: One-to-All Reachability (node 0 → all 341 others) ==="
+run_reachability_test "df_p3_one2all_MINIMAL" "$UEC_BIN" "$DF_P3" "MINIMAL" "$TEST_DIR/df_p3_one2all.tm" 341 "dragonfly"
+run_reachability_test "df_p3_one2all_SOURCE"  "$UEC_BIN" "$DF_P3" "SOURCE"  "$TEST_DIR/df_p3_one2all.tm" 341 "dragonfly"
+echo ""
+
+echo "=== Dragonfly p3a6h3: All-to-One Reachability (all 341 others → node 0) ==="
+run_reachability_test "df_p3_all2one_MINIMAL" "$UEC_BIN" "$DF_P3" "MINIMAL" "$TEST_DIR/df_p3_all2one.tm" 341 "dragonfly"
+run_reachability_test "df_p3_all2one_SOURCE"  "$UEC_BIN" "$DF_P3" "SOURCE"  "$TEST_DIR/df_p3_all2one.tm" 341 "dragonfly"
+echo ""
+
+echo "=== Dragonfly p3a6h3: Same-Switch (intra-switch) ==="
+run_reachability_test "df_p3_sameswitch_MINIMAL" "$UEC_BIN" "$DF_P3" "MINIMAL" "$TEST_DIR/df_p3_sameswitch.tm" 114 "dragonfly"
+run_reachability_test "df_p3_sameswitch_SOURCE"  "$UEC_BIN" "$DF_P3" "SOURCE"  "$TEST_DIR/df_p3_sameswitch.tm" 114 "dragonfly"
+echo ""
+
+echo "=== Dragonfly p3a6h3: Cross-Group (each group → opposite group) ==="
+run_reachability_test "df_p3_crossgroup_MINIMAL" "$UEC_BIN" "$DF_P3" "MINIMAL" "$TEST_DIR/df_p3_crossgroup.tm" 19 "dragonfly"
+run_reachability_test "df_p3_crossgroup_SOURCE"  "$UEC_BIN" "$DF_P3" "SOURCE"  "$TEST_DIR/df_p3_crossgroup.tm" 19 "dragonfly"
+echo ""
+
+echo "=== Dragonfly p3a6h3: Max Distance (group 0 ↔ last group) ==="
+run_reachability_test "df_p3_maxdist_MINIMAL" "$UEC_BIN" "$DF_P3" "MINIMAL" "$TEST_DIR/df_p3_maxdist.tm" 3 "dragonfly"
+run_reachability_test "df_p3_maxdist_SOURCE"  "$UEC_BIN" "$DF_P3" "SOURCE"  "$TEST_DIR/df_p3_maxdist.tm" 3 "dragonfly"
+echo ""
+
+# ============================================================
+# Slimfly p4q5 — MINIMAL & SOURCE routing
+# ============================================================
+SF_P4="$TOPO_DIR/slimfly/p4q5"
+
+echo "=== Slimfly p4q5: One-to-All Reachability (node 0 → all 199 others) ==="
+run_reachability_test "sf_p4_one2all_MINIMAL" "$UEC_BIN" "$SF_P4" "MINIMAL" "$TEST_DIR/sf_p4_one2all.tm" 199 "slimfly"
+run_reachability_test "sf_p4_one2all_SOURCE"  "$UEC_BIN" "$SF_P4" "SOURCE"  "$TEST_DIR/sf_p4_one2all.tm" 199 "slimfly"
+echo ""
+
+echo "=== Slimfly p4q5: All-to-One Reachability (all 199 others → node 0) ==="
+run_reachability_test "sf_p4_all2one_MINIMAL" "$UEC_BIN" "$SF_P4" "MINIMAL" "$TEST_DIR/sf_p4_all2one.tm" 199 "slimfly"
+run_reachability_test "sf_p4_all2one_SOURCE"  "$UEC_BIN" "$SF_P4" "SOURCE"  "$TEST_DIR/sf_p4_all2one.tm" 199 "slimfly"
+echo ""
+
+echo "=== Slimfly p4q5: Same-Switch (intra-switch) ==="
+run_reachability_test "sf_p4_sameswitch_MINIMAL" "$UEC_BIN" "$SF_P4" "MINIMAL" "$TEST_DIR/sf_p4_sameswitch.tm" 50 "slimfly"
+run_reachability_test "sf_p4_sameswitch_SOURCE"  "$UEC_BIN" "$SF_P4" "SOURCE"  "$TEST_DIR/sf_p4_sameswitch.tm" 50 "slimfly"
+echo ""
+
+echo "=== Slimfly p4q5: Cross-Partition (partition 0 → partition 1) ==="
+run_reachability_test "sf_p4_crosspart_MINIMAL" "$UEC_BIN" "$SF_P4" "MINIMAL" "$TEST_DIR/sf_p4_crosspart.tm" 25 "slimfly"
+run_reachability_test "sf_p4_crosspart_SOURCE"  "$UEC_BIN" "$SF_P4" "SOURCE"  "$TEST_DIR/sf_p4_crosspart.tm" 25 "slimfly"
+echo ""
+
+# ============================================================
+# Summary
+# ============================================================
+echo "========================================="
+echo "  REACHABILITY: $PASS passed / $FAIL failed / $TOTAL total"
+echo "========================================="
+if [ $FAIL -gt 0 ]; then
+    echo "SOME TESTS FAILED"
+    exit 1
+else
+    echo "ALL REACHABILITY TESTS PASSED"
+    exit 0
+fi