Parallel Test Execution

Parallel test execution allows you to run multiple tests simultaneously, reducing the total time required to execute a test suite. In Go, you can achieve parallel test execution using the built-in testing package.

Basic Parallel Test Execution

Here's a simple example demonstrating how to execute tests in parallel using Go's testing package:

package main

import (
	"testing"
	"time"
)

// Example test function that runs in parallel.
func TestExampleParallel(t *testing.T) {
	t.Parallel() // This indicates that this test is safe to run in parallel

	time.Sleep(1 * time.Second) // Simulate a test that takes 1 second
	t.Log("TestExampleParallel finished")
}

// Another example test function.
func TestAnotherExampleParallel(t *testing.T) {
	t.Parallel()

	time.Sleep(2 * time.Second) // Simulate a longer test
	t.Log("TestAnotherExampleParallel finished")
}

Running Sub-tests in Parallel

Go also allows sub-tests to be run in parallel. Here's how you can write tests with sub-tests that execute concurrently:

package main

import (
	"testing"
	"time"
)

func TestSubtestsParallel(t *testing.T) {
	tests := []struct {
		name string
	}{
		{"test1"},
		{"test2"},
		{"test3"},
	}

	for _, tt := range tests {
		tt := tt // capture range variable
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()
			time.Sleep(1 * time.Second)
			t.Logf("%s finished", tt.name)
		})
	}
}

Best Practices

• Avoid Shared State: Ensure that tests do not modify shared state, or use synchronization primitives if shared state is necessary.
• Use t.Parallel() Judiciously: Only mark tests as parallel if they are truly independent and do not affect each other, such as tests that do not modify global state.
• Resource Management: Consider the limits of your system resources (CPU, memory) when running tests in parallel to avoid resource exhaustion.

Common Pitfalls

• Race Conditions: Running tests in parallel can introduce race conditions if tests access shared data. Use Go's race detector (with go test -race) to identify and fix such issues.
• Test Order Dependence: Ensure that tests do not depend on the execution order, as parallel execution can change the order in which tests are run.
• Resource Contention: Be vigilant about tests competing for the same resources, which can lead to timeout failures.

Performance Tips

• Limited Parallelism: You can control the degree of parallelism using the -parallel flag with go test. Set it according to your hardware's capability to optimize performance (go test -parallel=4).
• Profile Test Runs: Use profiling tools to understand and optimize the performance of your test suite when parallelizing.
• Balance Test Duration: Aim to balance the duration of parallel tests so that no single test becomes a bottleneck, ensuring optimal resource usage and reduced execution time.