Supertester

A battle-hardened testing toolkit for building robust and resilient Elixir & OTP applications.

The Problem: Flaky OTP Tests

Are you tired of...

• 😫 Flaky tests that fail randomly due to race conditions?
• 📛 GenServer name clashes when running tests with async: true?
• 🕰️ Littering your test suite with Process.sleep/1 and hoping for the best?
• 🤷‍♂️ Struggling to test process crashes, restarts, and complex supervision trees?

Writing tests for concurrent systems is hard. Traditional testing methods often lead to fragile, non-deterministic, and slow test suites.

The Solution: Supertester

Supertester provides a comprehensive suite of tools to write clean, deterministic, and reliable tests for your OTP applications. It replaces fragile timing hacks with robust synchronization patterns and provides powerful helpers for simulating and asserting complex OTP behaviors.

With Supertester, you can build a test suite that is fast, parallel, and trustworthy.

Key Features

• ✅ Rock-Solid Test Isolation: Run all your tests with async: true without fear of process name collisions or state leakage.
• 🔄 Deterministic Synchronization: No more Process.sleep/1. Use helpers that wait for processes to be ready, casts to be processed, and supervisors to stabilize.
• 🤖 Powerful OTP Assertions: Go beyond assert. Use assert_process_restarted/2, assert_genserver_state/2, and assert_all_children_alive/1 for more expressive tests.
• ✨ Effortless Setup & Teardown: Start isolated GenServers and Supervisors with a single line and trust Supertester to handle all the cleanup.
• 💥 Resilience & Chaos Testing: Tools for testing crash recovery, supervision strategies, and system stability under stress.

Installation

Add supertester as a dependency in your mix.exs file. It's only needed for the :test environment.

def deps do
  [
    {:supertester, "~> 0.1.0", only: :test}
  ]
end

Then, run mix deps.get to install.

Quick Start: From Flaky to Robust

See how Supertester transforms a common, fragile test pattern into a robust, deterministic one.

Before: The Flaky Way

# test/my_app/counter_test.exs
defmodule MyApp.CounterTest do
  use ExUnit.Case, async: false # <-- Forced to run sequentially

  test "incrementing the counter" do
    # Manual setup, prone to name conflicts
    {:ok, _pid} = start_supervised({Counter, name: Counter})

    GenServer.cast(Counter, :increment)
    Process.sleep(50) # <-- Fragile, timing-dependent guess

    state = GenServer.call(Counter, :state)
    assert state.count == 1
  end
end

After: The Supertester Way

# test/my_app/counter_test.exs
defmodule MyApp.CounterTest do
  use ExUnit.Case, async: true # <-- Fully parallel!

  # Import the tools you need
  import Supertester.OTPHelpers
  import Supertester.GenServerHelpers
  import Supertester.Assertions

  test "incrementing the counter" do
    # Isolated setup with automatic cleanup, no name clashes
    {:ok, counter_pid} = setup_isolated_genserver(Counter)

    # Deterministic sync: ensures the cast is processed before continuing
    :ok = cast_and_sync(counter_pid, :increment)

    # Expressive, OTP-aware assertion for checking state
    assert_genserver_state(counter_pid, fn state -> state.count == 1 end)
  end
end

Core API Highlights

Supertester is organized into several modules, each targeting a specific area of OTP testing.

Supertester.OTPHelpers

For setting up and managing isolated OTP processes.

• setup_isolated_genserver/3: Starts a GenServer with a unique name and automatic cleanup.
• setup_isolated_supervisor/3: Starts a Supervisor with a unique name and automatic cleanup.
• wait_for_process_restart/3: Blocks until a supervised process has been terminated and restarted.
• wait_for_genserver_sync/2: Ensures a GenServer is alive and responsive.

Supertester.GenServerHelpers

For interacting with and testing GenServers.

• cast_and_sync/3: Sends a cast and waits for a follow-up call to confirm it was processed.
• get_server_state_safely/1: Fetches GenServer state without crashing if the process is down.
• test_server_crash_recovery/2: Simulates a process crash and verifies its recovery by the supervisor.
• concurrent_calls/3: Stress-tests a GenServer with many concurrent requests.

Supertester.Assertions

Custom, OTP-aware assertions for more meaningful tests.

• assert_process_alive/1 & assert_process_dead/1
• assert_genserver_state/2: Asserts the GenServer's internal state matches a value or passes a function check.
• assert_child_count/2: Asserts a supervisor has an exact number of active children.
• assert_all_children_alive/1: Checks that all children in a supervision tree are running.
• assert_no_process_leaks/1: Ensures an operation cleans up all the processes it spawns.

Supertester.UnifiedTestFoundation

Provides advanced, case-level isolation for complex scenarios.

defmodule MyApp.MyAdvancedTest do
  use ExUnit.Case
  # Choose an isolation level for the entire test module.
  # :full_isolation provides sandboxed processes and ETS tables.
  use Supertester.UnifiedTestFoundation, isolation: :full_isolation

  test "this test runs in a complete sandbox", context do
    # `context.isolation_context` holds info about the sandbox.
    # All processes started via Supertester helpers are tracked and auto-cleaned.
    {:ok, server} = Supertester.OTPHelpers.setup_isolated_genserver(MyServer)
    # ... your isolated test logic ...
  end
end

Contributing

Contributions are welcome! If you'd like to help improve Supertester, please feel free to:

1. Fork the repository.
2. Create a new feature branch.
3. Add your feature or bug fix.
4. Ensure all new code is covered by tests.
5. Open a pull request.

License

This project is licensed under the MIT License.