feat: add a fuzzing test

fuzz/.gitignore

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+target
+corpus
+artifacts
+coverage
+afl.rs

fuzz/Cargo.toml

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+[package]
+name = "coinselect_rust-coinselect-fuzz"
+version = "0.0.0"
+publish = false
+edition = "2021"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.4"
+arbitrary = {version="1.4", features=["derive"]}
+
+[dependencies.rust-coinselect]
+path = ".."
+
+[[bin]]
+name = "coinselect"
+path = "fuzz_targets/coinselect.rs"
+test = false
+doc = false
+bench = false

fuzz/fuzz_targets/coinselect.rs

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+#![no_main]
+
+use arbitrary::{Arbitrary, Unstructured};
+use libfuzzer_sys::fuzz_target;
+use rust_coinselect::{
+    selectcoin::select_coin,
+    types::{CoinSelectionOpt, ExcessStrategy, OutputGroup},
+};
+
+#[derive(Debug, Arbitrary)]
+pub struct ArbitraryOutputGroup {
+    pub value: u64,
+    pub weight: u64,
+    pub input_count: usize,
+    pub creation_sequence: Option<u32>,
+}
+
+impl Into<OutputGroup> for ArbitraryOutputGroup {
+    fn into(self) -> OutputGroup {
+        OutputGroup {
+            value: self.value,
+            weight: self.weight,
+            input_count: self.input_count,
+            creation_sequence: self.creation_sequence,
+        }
+    }
+}
+
+#[derive(Debug, Arbitrary)]
+pub struct ArbitraryCoinSelectionOpt {
+    pub target_value: u64,
+    pub target_feerate: f32,
+    pub long_term_feerate: Option<f32>,
+    pub min_absolute_fee: u64,
+    pub base_weight: u64,
+    pub change_weight: u64,
+    pub change_cost: u64,
+    pub avg_input_weight: u64,
+    pub avg_output_weight: u64,
+    pub min_change_value: u64,
+    pub excess_strategy: ArbitraryExcessStrategy,
+}
+
+impl Into<CoinSelectionOpt> for ArbitraryCoinSelectionOpt {
+    fn into(self) -> CoinSelectionOpt {
+        CoinSelectionOpt {
+            target_value: self.target_value,
+            target_feerate: self.target_feerate,
+            long_term_feerate: self.long_term_feerate,
+            min_absolute_fee: self.min_absolute_fee,
+            base_weight: self.base_weight,
+            change_weight: self.change_weight,
+            change_cost: self.change_cost,
+            avg_input_weight: self.avg_input_weight,
+            avg_output_weight: self.avg_output_weight,
+            min_change_value: self.min_change_value,
+            excess_strategy: self.excess_strategy.into(),
+        }
+    }
+}
+#[derive(Debug, Arbitrary)]
+pub enum ArbitraryExcessStrategy {
+    ToFee,
+    ToRecipient,
+    ToChange,
+}
+
+impl Into<ExcessStrategy> for ArbitraryExcessStrategy {
+    fn into(self) -> ExcessStrategy {
+        match self {
+            ArbitraryExcessStrategy::ToFee => ExcessStrategy::ToFee,
+            ArbitraryExcessStrategy::ToChange => ExcessStrategy::ToChange,
+            ArbitraryExcessStrategy::ToRecipient => ExcessStrategy::ToRecipient,
+        }
+    }
+}
+
+fuzz_target!(|data: &[u8]| {
+    let mut u = Unstructured::new(&data);
+    let arbitrary_inputs = Vec::<ArbitraryOutputGroup>::arbitrary(&mut u).unwrap();
+    let mut inputs = Vec::new();
+    for o in arbitrary_inputs {
+        inputs.push(o.into());
+    }
+    let opts = ArbitraryCoinSelectionOpt::arbitrary(&mut u).unwrap().into();
+    dbg!(&inputs);
+    dbg!(&opts);
+    let _ = select_coin(&inputs, &opts);
+});