Assert the evidence that matters

Use ordinary Python assertions for direct operation results. Use expect when you need to ask a question about a complete M3 execution or agent turn.

Direct result

with MCPTestKit(env={}) as kit, kit.direct(server) as client:
    result = client.call_tool("shipping_quote", {"weight_kg": 2, "zone": "local"}
    )

assert result.is_error is False
assert result.structured_content == {"amount": 9.0, "currency": "USD"}

This checks the server response directly.

Agent evidence

from m3 import expect

result = agent.run("Quote a 2 kg parcel in the local zone.",
    server=server,
    permission_policy="allow",
)

expect(result).to_have_tool_call("shipping_quote", arguments={"weight_kg": 2, "zone": "local"},
    status="success",
)

This checks the captured call, its arguments, and its result status. It does not accept the agent's prose as proof that the call occurred. Grant tool approval only to the scoped test server and workspace.

See the matcher reference for count, choice, and result predicates.