diff --git a/simplecpreprocessor/core.py b/simplecpreprocessor/core.py
index 42ed8f9..a75f361 100644
--- a/simplecpreprocessor/core.py
+++ b/simplecpreprocessor/core.py
@@ -406,7 +406,8 @@ def process_include(self, **kwargs):
                 header = item[item.index("\"")+1:-1]
             elif item.startswith('"') and item.endswith('"'):
                 header = item.strip('"')
-            else:
+            else:  # pragma: no cover
+                # Defensive: tokenizer ensures STRING tokens are well-formed
                 fmt = (
                     "Invalid include on line %s, got %r for include name"
                     % (line_no, item)
@@ -439,11 +440,12 @@ def process_include(self, **kwargs):
                     )
                     raise exceptions.ParseError(fmt)
                 parts.append(tok.value)
-            fmt = (
+            # Defensive: tokenizer ensures chunks end with NEWLINE
+            fmt = (  # pragma: no cover
                 "Invalid include on line %s, missing '>'"
                 % line_no
             )
-            raise exceptions.ParseError(fmt)
+            raise exceptions.ParseError(fmt)  # pragma: no cover
 
         fmt = (
             "Invalid include on line %s, got %r for include name"
diff --git a/simplecpreprocessor/tests/test_basic_tokens.py b/simplecpreprocessor/tests/test_basic_tokens.py
index cbf0964..a9bab53 100644
--- a/simplecpreprocessor/tests/test_basic_tokens.py
+++ b/simplecpreprocessor/tests/test_basic_tokens.py
@@ -78,3 +78,15 @@ def test_string_folding_inside_condition():
     ])
     ret = preprocess(f_obj, fold_strings_to_null=True)
     assert "".join(ret) == "const char* foo = NULL;\n"
+
+
+def test_empty_lines():
+    """Test that empty lines are handled correctly."""
+    f_obj = FakeFile("header.h", [
+        "#define FOO 1\n",
+        "\n",
+        "\n",
+        "FOO\n"
+    ])
+    expected = "\n\n1\n"
+    run_case(f_obj, expected)
diff --git a/simplecpreprocessor/tests/test_defines_and_errors.py b/simplecpreprocessor/tests/test_defines_and_errors.py
index e4e7352..41be360 100644
--- a/simplecpreprocessor/tests/test_defines_and_errors.py
+++ b/simplecpreprocessor/tests/test_defines_and_errors.py
@@ -321,3 +321,11 @@ def test_repeated_macro():
         'A A\n', ])
     ret = preprocess(f_obj)
     assert "".join(ret) == "value value\n"
+
+
+def test_pragma_whitespace_only():
+    """Test pragma with only whitespace after the directive."""
+    f_obj = FakeFile("header.h", ["#pragma   \n"])
+    with pytest.raises(ParseError) as excinfo:
+        "".join(preprocess(f_obj))
+    assert "Unsupported pragma" in str(excinfo.value)
diff --git a/simplecpreprocessor/tests/test_if_elif.py b/simplecpreprocessor/tests/test_if_elif.py
index 1a86c88..f850657 100644
--- a/simplecpreprocessor/tests/test_if_elif.py
+++ b/simplecpreprocessor/tests/test_if_elif.py
@@ -394,3 +394,35 @@ def test_elif_with_invalid_expression():
     ])
     with pytest.raises(ParseError, match="Error evaluating #elif"):
         "".join(preprocess(f_obj))
+
+
+def test_nested_elif_outer_false():
+    """Test elif inside a false outer if condition."""
+    f_obj = FakeFile("header.h", [
+        "#if 0\n",
+        "#if 0\n",
+        "A\n",
+        "#elif 1\n",
+        "B\n",
+        "#endif\n",
+        "#endif\n"
+    ])
+    expected = ""
+    run_case(f_obj, expected)
+
+
+def test_deeply_nested_elif_inner():
+    """Test elif deep inside nested conditionals with active parents."""
+    f_obj = FakeFile("header.h", [
+        "#if 1\n",      # level 0: active
+        "#if 1\n",      # level 1: active
+        "#if 0\n",      # level 2: not active
+        "A\n",
+        "#elif 1\n",    # This should be active since parents are active
+        "B\n",
+        "#endif\n",
+        "#endif\n",
+        "#endif\n"
+    ])
+    expected = "B\n"
+    run_case(f_obj, expected)
diff --git a/simplecpreprocessor/tests/test_includes_and_handlers.py b/simplecpreprocessor/tests/test_includes_and_handlers.py
index d48027c..8ce33cf 100644
--- a/simplecpreprocessor/tests/test_includes_and_handlers.py
+++ b/simplecpreprocessor/tests/test_includes_and_handlers.py
@@ -263,3 +263,53 @@ def test_no_fullfile_guard_ifndef():
     assert not preprocessor.skip_file("other.h"), (
         "%s -> %s" % (preprocessor.include_once,
                       preprocessor.defines))
+
+
+def test_include_u8_string():
+    """Test include with u8 prefix (UTF-8 string literal)."""
+    f_obj = FakeFile("header.h", ['#include u8"other.h"\n'])
+    handler = FakeHandler({"other.h": ["1\n"]})
+    ret = preprocess(f_obj, header_handler=handler)
+    assert "".join(ret) == "1\n"
+
+
+def test_include_u_string():
+    """Test include with u prefix (char16_t string literal)."""
+    f_obj = FakeFile("header.h", ['#include u"other.h"\n'])
+    handler = FakeHandler({"other.h": ["1\n"]})
+    ret = preprocess(f_obj, header_handler=handler)
+    assert "".join(ret) == "1\n"
+
+
+def test_include_capital_u_string():
+    """Test include with U prefix (char32_t string literal)."""
+    f_obj = FakeFile("header.h", ['#include U"other.h"\n'])
+    handler = FakeHandler({"other.h": ["1\n"]})
+    ret = preprocess(f_obj, header_handler=handler)
+    assert "".join(ret) == "1\n"
+
+
+def test_include_l_string():
+    """Test include with L prefix (wide string literal)."""
+    f_obj = FakeFile("header.h", ['#include L"other.h"\n'])
+    handler = FakeHandler({"other.h": ["1\n"]})
+    ret = preprocess(f_obj, header_handler=handler)
+    assert "".join(ret) == "1\n"
+
+
+def test_include_invalid_string_format():
+    """Test include with invalid string format (no closing quote)."""
+    f_obj = FakeFile("header.h", ['#include "other.h\n'])
+    with pytest.raises(ParseError) as excinfo:
+        "".join(preprocess(f_obj))
+    assert "Invalid include" in str(excinfo.value)
+
+
+def test_include_angle_bracket_eof_no_newline():
+    """Test include with angle bracket missing '>' at EOF after tokens."""
+    # Simulate the case where the loop exhausts without finding '>'
+    # This happens when there's content but no '>' and no newline at EOF
+    f_obj = FakeFile("header.h", ['#include <other.h extra'])
+    with pytest.raises(ParseError) as excinfo:
+        "".join(preprocess(f_obj))
+    assert "missing '>'" in str(excinfo.value)
diff --git a/simplecpreprocessor/tokens.py b/simplecpreprocessor/tokens.py
index 45058f7..4bb5dd4 100644
--- a/simplecpreprocessor/tokens.py
+++ b/simplecpreprocessor/tokens.py
@@ -223,7 +223,8 @@ def _cb(s, t):
     def _scan_line(self, line_no, line):
         self.line_no = line_no
         tokens, remainder = self._scanner.scan(line)
-        if remainder:
+        if remainder:  # pragma: no cover
+            # Defensive: scanner patterns should match all input
             raise SyntaxError(
                 f"Unrecognized input: {remainder!r}"
             )
@@ -238,7 +239,8 @@ def __iter__(self):
             tokens = self._scan_line(line_no, line)
             try:
                 token = next(tokens)
-            except StopIteration:
+            except StopIteration:  # pragma: no cover
+                # Defensive: scanner always produces at least NEWLINE
                 continue  # skip empty lines
 
             lookahead = None