diff --git a/tests/test_mermaid_generator.py b/tests/test_mermaid_generator.py
new file mode 100644
index 0000000..62ea852
--- /dev/null
+++ b/tests/test_mermaid_generator.py
@@ -0,0 +1,85 @@
+from pathlib import Path
+from codemap.core import GraphBuilder, MermaidGenerator
+from codemap.parsers import ParsedFile
+
+
+def test_mermaid_generator_basic():
+    builder = GraphBuilder()
+
+    files = [
+        ParsedFile(file_path=Path("/app/main.py"), module_name="main", dependencies=[], file_type="python"),
+        ParsedFile(file_path=Path("/app/utils.py"), module_name="utils", dependencies=[], file_type="python"),
+    ]
+
+    builder.build_from_files(files)
+    graph_data = builder.get_graph_data()
+
+    generator = MermaidGenerator(graph_data)
+    output = generator.generate_flowchart()
+
+    assert "graph TD" in output
+    assert "main" in output
+    assert "utils" in output
+
+
+def test_mermaid_generator_with_packages():
+    builder = GraphBuilder()
+
+    files = [
+        ParsedFile(file_path=Path("/app/src/main.py"), module_name="main", dependencies=[], file_type="python"),
+        ParsedFile(file_path=Path("/app/src/utils.py"), module_name="utils", dependencies=[], file_type="python"),
+    ]
+
+    builder.build_from_files(files)
+    graph_data = builder.get_graph_data()
+
+    generator = MermaidGenerator(graph_data)
+    output = generator.generate_flowchart(include_packages=True)
+
+    assert "subgraph" in output
+
+
+def test_mermaid_generator_class_diagram():
+    builder = GraphBuilder()
+
+    files = [
+        ParsedFile(file_path=Path("/app/main.py"), module_name="main", dependencies=[], file_type="python"),
+    ]
+
+    builder.build_from_files(files)
+    graph_data = builder.get_graph_data()
+
+    generator = MermaidGenerator(graph_data)
+    output = generator.generate_class_diagram()
+
+    assert "classDiagram" in output
+
+
+def test_mermaid_generator_pie_chart():
+    builder = GraphBuilder()
+
+    files = [
+        ParsedFile(file_path=Path("/app/main.py"), module_name="main", dependencies=[], file_type="python"),
+        ParsedFile(file_path=Path("/app/main.js"), module_name="main", dependencies=[], file_type="javascript"),
+        ParsedFile(file_path=Path("/app/main.go"), module_name="main", dependencies=[], file_type="go"),
+    ]
+
+    builder.build_from_files(files)
+    graph_data = builder.get_graph_data()
+
+    generator = MermaidGenerator(graph_data)
+    output = generator.generate_pie_chart()
+
+    assert "pie" in output
+    assert "python" in output
+    assert "javascript" in output
+    assert "go" in output
+
+
+def test_safe_id():
+    builder = GraphBuilder()
+    generator = MermaidGenerator(builder.get_graph_data())
+
+    safe = generator._safe_id("/app/my-project/file.name.js")
+    assert " " not in safe
+    assert safe[0].isalpha() or safe[0] == "_"