Add comprehensive test suite (104 tests)

Tests cover:
- VFS: sandbox escape, path traversal, CRUD, singleton staleness
- Config loader: missing keys, temperature cascade, oversight fallback
- Tools: schema/implementation sync, VFS delegation
- Agent: message construction, error handling, token counting, reasoning extraction
- Interrogation: sanitization, provider detection, prompt loading
- Runner: baseline extraction, prompt assembly, success detection

All tests run offline with mocked API calls.

1 files changed, 72 insertions, 0 deletions

diff --git a/tests/test_tools.py b/tests/test_tools.py
new file mode 100644
index 0000000..a4832ff
--- /dev/null
+++ b/tests/test_tools.py
@@ -0,0 +1,72 @@
+"""
+Tests for tools.py — schema/implementation sync, delegation to VFS.
+"""
+import pytest
+from vfs import VFS
+from tools import tools, available_functions, list_files, create_file, read_file, delete_file
+
+
+class TestToolSchemaSync:
+    """The tool JSON schema and available_functions dict MUST stay in sync.
+    If they drift, the agent calls a tool that doesn't exist or vice versa.
+    """
+
+    def test_all_schemas_have_implementations(self):
+        """Every tool in the schema list must have a matching function."""
+        schema_names = {t["function"]["name"] for t in tools}
+        impl_names = set(available_functions.keys())
+        missing = schema_names - impl_names
+        assert not missing, f"Tools defined in schema but not implemented: {missing}"
+
+    def test_all_implementations_have_schemas(self):
+        """Every implemented function must have a schema (otherwise LLM can't call it)."""
+        schema_names = {t["function"]["name"] for t in tools}
+        impl_names = set(available_functions.keys())
+        extra = impl_names - schema_names
+        assert not extra, f"Functions implemented but not in schema: {extra}"
+
+    def test_schema_structure(self):
+        """Each tool schema must have the required OpenAI function-calling fields."""
+        for tool in tools:
+            assert tool["type"] == "function"
+            func = tool["function"]
+            assert "name" in func
+            assert "description" in func
+            assert "parameters" in func
+            assert func["parameters"]["type"] == "object"
+            assert "properties" in func["parameters"]
+            assert "required" in func["parameters"]
+
+
+class TestToolFunctions:
+    """Tool functions are thin wrappers around VFS. Make sure they delegate correctly."""
+
+    def setup_method(self):
+        VFS._instance = None
+        VFS.get_instance()
+
+    def test_create_and_read(self):
+        create_file("/test.txt", "hello")
+        assert read_file("/test.txt") == "hello"
+
+    def test_list_files(self):
+        create_file("/a.txt", "a")
+        create_file("/b.txt", "b")
+        result = list_files("/")
+        assert "a.txt" in result
+        assert "b.txt" in result
+
+    def test_delete_file(self):
+        create_file("/temp.txt", "data")
+        result = delete_file("/temp.txt")
+        assert "deleted" in result
+        assert read_file("/temp.txt") == "File not found or is a directory."
+
+    def test_create_file_missing_arg_raises(self):
+        """Calling create_file without content should raise TypeError."""
+        with pytest.raises(TypeError):
+            create_file("/file.txt")
+
+    def test_read_file_missing_arg_raises(self):
+        with pytest.raises(TypeError):
+            read_file()