Run the snippets test suite.

def snippets(session):
    """Run the snippets test suite."""

    # Sanity check: Only run snippets tests if the environment variable is set.
    if not os.environ.get("GOOGLE_APPLICATION_CREDENTIALS", ""):
        session.skip("Credentials must be set via environment variable.")

    # Install all test dependencies, then install local packages in place.
    session.install("mock", "pytest")
    for local_dep in LOCAL_DEPS:
        session.install("-e", local_dep)
    session.install("-e", os.path.join("..", "storage"))
    session.install("-e", os.path.join("..", "test_utils"))
    session.install("-e", ".[all]")

    # Run py.test against the snippets tests.
    session.run("py.test", os.path.join("docs", "snippets.py"), *session.posargs)
    session.run("py.test", "samples", *session.posargs)