pytest-fly 0.3.37

pytest runner and observer

pytest-fly

pytest-fly aids the development, debug, and execution of complex code bases and test suites.

Features

• Real-time monitoring of test execution in a GUI with six tabs:
  • Run — start/stop controls, run mode selection (Restart/Resume/Check), and several panels: a Status panel (completion percentage, pass rate, per-state counts, elapsed time, average parallelism, coverage, and estimated time remaining), a System Performance panel (live CPU and memory charts, with memory shown as used/total GB alongside percent), a Failed Tests panel with clipboard copy, and program-under-test version/dirty-git indicators
  • Graph — time-based progress chart showing each test module as a horizontal bar
  • Table — per-test status grid with elapsed time, peak CPU, memory usage, and individual coverage
  • Coverage — line chart of combined code coverage over time with covered/total line counts
  • Configuration — parallelism settings, refresh rate, and utilization thresholds
  • About — system and project information
• Parallel test execution at the module level with configurable process count.
• Three run modes — Restart (rerun all tests), Resume (skip already-passed tests and only re-run failed or unrun tests), and Check (resume if the program under test has not changed, otherwise restart).
• Graceful interruption — stop the test suite and resume where it left off.
• Per-process resource monitoring — tracks peak CPU and memory usage for each test module.
• Estimated time remaining based on prior run durations, accounting for parallelism.
• Code coverage tracking — each test writes its own coverage data, combined automatically as tests complete. The Coverage tab plots coverage over time, and the Table shows per-test coverage. Coverage persists across restarts so previously-passed tests contribute to the total.
• Singleton test support via @pytest.mark.singleton — singleton tests run exclusively with no other tests executing concurrently.

Installation

You can install pytest-fly via pip from PyPI:

pip install pytest-fly

Parallelism

By default, pytest-fly executes modules (.py files) in parallel.

Functions inside a module are executed serially with respect to each other. No parallelism is performed for functions inside a module. For example, if a set of tests use a shared resource that does not support concurrent access, putting those tests in the same module ensures the tests do not conflict.

Modules can optionally be marked as a singleton via the @pytest.mark.singleton marker. When a singleton test runs, all other workers wait until it completes before starting new tests. This is enforced at runtime, not just by scheduling order.

In pytest terms, each module is run in a separate subprocess. Therefore, a pytest fixture with a session scope will actually be executed multiple times, once for each module.

Note that test concurrency in pytest-fly is different from pytest-xdist. group-by in pytest-xdist is analogous to putting the tests in the same module in pytest-fly.

Test Scheduling

pytest-fly orders tests to surface actionable information earlier:

1. When Prioritize Never-Run Tests is enabled in the Configuration tab, tests with no record in the database (across any program-under-test version) are promoted to the front of the queue, giving developers adding new tests immediate feedback. This takes precedence over failed-first and coverage-efficiency ordering.
2. Tests that failed in the prior run are re-run first, so developers get faster feedback on tests they are likely fixing.
3. When prior run data is available, tests with higher coverage efficiency (lines/second) are run earlier. This way, if there is a problem in the code, it is more likely to be found earlier in the test run.
4. singleton tests are run last to maximize parallel throughput before exclusive execution begins.