pytest-mcp-assert
pytest plugin for mcp-assert. Run MCP server assertions as pytest test items.
Install
pip install pytest-mcp-assert
You also need the mcp-assert binary. Any of these:
brew install blackwell-systems/tap/mcp-assert
pip install mcp-assert
npm install -g @blackwell-systems/mcp-assert
Usage
Write assertion YAML files (see mcp-assert docs):
# evals/echo.yaml
name: echo returns the message
server:
command: my-mcp-server
assert:
tool: echo
args:
message: hello
expect:
not_error: true
contains: ["hello"]
timeout: 30s
Run with pytest:
pytest --mcp-suite evals/
Each YAML file becomes a pytest test item with pass/fail/skip semantics.
Options
| Option | pyproject.toml | Description |
|---|---|---|
--mcp-suite DIR |
mcp_suite |
Directory containing assertion YAML files |
--mcp-fixture DIR |
mcp_fixture |
Fixture directory (substituted for {{fixture}}) |
--mcp-server CMD |
Override server command for all assertions | |
--mcp-timeout DUR |
mcp_timeout |
Per-assertion timeout (default: 30s) |
--mcp-binary PATH |
Path to mcp-assert binary |
Configuration
# pyproject.toml
[tool.pytest.ini_options]
mcp_suite = "evals/"
mcp_fixture = "fixtures/"
mcp_timeout = "30s"
Then just run pytest with no extra flags.
How it works
The plugin discovers .yaml files in the suite directory, creates a pytest Item for each one, and calls mcp-assert run --suite <file> --json to execute it. The JSON result is mapped to pytest outcomes:
status: "pass"becomes a pytest passstatus: "fail"becomes a pytest failure with the detail as the messagestatus: "skip"becomes a pytest skipskip: truein the YAML skips the test (for known bugs)
The Go binary handles all MCP protocol interaction. The plugin is a thin bridge.
1 maintainer
Metadata
1 maintainer
Release files for pytest-mcp-assert 0.12.3
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Release files / pytest_mcp_assert-0.12.3.tar.gz
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