test: greet input-bound enforcement

tests/test_tools.py

@@ -1,5 +1,8 @@
 """Tests for MCP server tools."""
 
+import pytest
+from pydantic import ValidationError, validate_call
+
 from my_mcp_server.server import greet
 
 
@@ -13,3 +16,31 @@ async def test_greet_custom_name():
     """Greet handles custom names."""
     result = await greet(name="Ploidy")
     assert result == "Hello, Ploidy!"
+
+
+# --- input bound enforcement -----------------------------------------------
+# Calling the tool function directly bypasses FastMCP's protocol-level
+# schema validation. Wrapping with `validate_call` is the same enforcement
+# FastMCP applies, so we cover Annotated[..., Field(min_length, max_length)]
+# without spinning up the MCP transport.
+
+_validated_greet = validate_call(greet)
+
+
+async def test_greet_rejects_empty_name():
+    """min_length=1 — empty string must be rejected at the protocol layer."""
+    with pytest.raises(ValidationError):
+        await _validated_greet(name="")
+
+
+async def test_greet_rejects_oversize_name():
+    """max_length=200 — long strings must be rejected."""
+    with pytest.raises(ValidationError):
+        await _validated_greet(name="x" * 201)
+
+
+async def test_greet_accepts_boundary_lengths():
+    """1 and 200 are inclusive bounds and must pass."""
+    assert await _validated_greet(name="a") == "Hello, a!"
+    long_name = "a" * 200
+    assert await _validated_greet(name=long_name) == f"Hello, {long_name}!"