How to Write Fuzz Tests in Go (Go 1.18+)

Write a fuzz test function named Fuzz<Name> that accepts a *testing.F argument, add seed inputs with f.Add, and define the fuzzing logic inside f.Fuzz.

func FuzzReader(f *testing.F) {
	// Add a valid seed input
	f.Add([]byte("valid input data"))

	f.Fuzz(func(t *testing.T, data []byte) {
		// Your code under test
		// Example: r := NewReader(bytes.NewReader(data))
		// If parsing fails, return early to skip this iteration
		if err := r.Read(); err != nil {
			return
		}
		// Add assertions or checks here
	})
}

Run the test with go test -fuzz=FuzzReader ./....

Fuzzing is an automated testing technique that feeds random, malformed, or unexpected data into your program to find crashes or security bugs. It matters because it uncovers edge cases that standard tests miss, acting like a stress test that tries to break your code with garbage input. You use it when you need to ensure your parser or data handler is robust against bad input.