Helper Functions & Fixtures

This guide covers built-in helper functions and auxiliary fixtures provided by pytest-embedded.

redirect Fixture

The redirect fixture allows you to redirect Python console output (sys.stdout) into the internal DUT message queue. This is useful for writing simulated inputs, logging test steps, or verifying output redirection.

def test_redirect_example(dut, redirect):
    with redirect():
        print("Simulated device response")

    dut.expect("Simulated device response")

log_metric Fixture

The log_metric fixture records numeric benchmarks (such as boot duration, heap memory usage, or transfer speeds) during test runs. It writes data following the Prometheus / OpenMetrics text format.

Use Case

Use log_metric to track performance over time across firmware revisions and detect regressions in CI.

Enabling Metric Logging

Provide the --metric-path CLI option to specify where metrics are saved:

pytest --metric-path output/metrics.txt

Usage Example

Include log_metric as an argument in your test function:

def test_performance(log_metric):
    boot_time_ms = 142.5
    free_heap_kb = 230

    # Record metric with key, numeric value, and optional labels
    log_metric("boot_duration_ms", boot_time_ms, target="esp32s3", config="release")
    log_metric("free_heap_kb", free_heap_kb, target="esp32s3")

Output Format

The recorded file follows the Prometheus text format:

boot_duration_ms{target="esp32s3",config="release"} 142.5
free_heap_kb{target="esp32s3"} 230

Note

If --metric-path is not specified, log_metric issues a UserWarning and performs no file writing.

Test Context & Metadata Fixtures

pytest-embedded provides several fixtures to query test session metadata:

• test_case_name: Returns the name of the current test function as a string (e.g. "test_performance").

• test_file_path: Returns the absolute path to the currently executing test Python script.

• session_root_logdir: Returns the root directory path where log files for the current pytest session are stored. Configured via --root-logdir.

• session_temp_dir: Returns the temporary directory created for the active test session.

Example:

def test_metadata(test_case_name, test_file_path, session_root_logdir):
    print(f"Executing: {test_case_name}")
    print(f"File: {test_file_path}")
    print(f"Logs stored in: {session_root_logdir}")