Go Test Benchmark

In this tutorial, you'll learn about Go Test: Benchmarking. We cover key concepts, practical examples, and best practices.

Benchmark testing -- Write accurate Go benchmarks using the correct b.N iteration pattern.

The Problem

Go benchmarks must use b.N for the loop count. The testing framework adjusts b.N for stable timing. Expensive setup should be outside the loop using b.ResetTimer().

Wrong

func BenchmarkBad(b *testing.B) {
    for i := 0; i < 1000; i++ { // Wrong! Fixed iteration count
        expensiveOp()
    }
}

Output:

// Not a valid benchmark. Does not measure correctly.

Right

func BenchmarkGood(b *testing.B) {
    data := setupData() // Expensive setup
    b.ResetTimer()      // Don't count setup
    for i := 0; i < b.N; i++ {
        expensiveOp(data)
    }
}

Output:

$ go test -bench=. -benchmem
BenchmarkGood-8    1000000  1234 ns/op  256 B/op  3 allocs/op

Prevention

• Always use b.N for loop iteration count
• Use b.ResetTimer() after expensive setup
• Use b.ReportAllocs() or -benchmem for alloc stats
• Use b.RunParallel() for concurrent benchmarks
• Multiple sub-benchmarks with b.Run()

Common Mistakes with test benchmark

1. Using return to exit a function early instead of wrapping a pure value in the monad
2. Mixing let bindings with <- bindings in do notation, producing type errors
3. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors

These mistakes appear frequently in real-world GO code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ

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