Testing and Benchmarking #

// Unit testing is an important part of writing
// principled Go programs. The `testing` package
// provides the tools we need to write unit tests
// and the `go test` command runs tests.

// For the sake of demonstration, this code is in package
// `main`, but it could be any package. Testing code
// typically lives in the same package as the code it tests.
package main

import (
	"fmt"
	"testing"
)

// We'll be testing this simple implementation of an
// integer minimum. Typically, the code we're testing
// would be in a source file named something like
// `intutils.go`, and the test file for it would then
// be named `intutils_test.go`.
func IntMin(a, b int) int {
	if a < b {
		return a
	}
	return b
}

// A test is created by writing a function with a name
// beginning with `Test`.
func TestIntMinBasic(t *testing.T) {
	ans := IntMin(2, -2)
	if ans != -2 {
		// `t.Error*` will report test failures but continue
		// executing the test. `t.Fatal*` will report test
		// failures and stop the test immediately.
		t.Errorf("IntMin(2, -2) = %d; want -2", ans)
	}
}

// Writing tests can be repetitive, so it's idiomatic to
// use a *table-driven style*, where test inputs and
// expected outputs are listed in a table and a single loop
// walks over them and performs the test logic.
func TestIntMinTableDriven(t *testing.T) {
	var tests = []struct {
		a, b int
		want int
	}{
		{0, 1, 0},
		{1, 0, 0},
		{2, -2, -2},
		{0, -1, -1},
		{-1, 0, -1},
	}

	for _, tt := range tests {
		// t.Run enables running "subtests", one for each
		// table entry. These are shown separately
		// when executing `go test -v`.
		testname := fmt.Sprintf("%d,%d", tt.a, tt.b)
		t.Run(testname, func(t *testing.T) {
			ans := IntMin(tt.a, tt.b)
			if ans != tt.want {
				t.Errorf("got %d, want %d", ans, tt.want)
			}
		})
	}
}

// Benchmark tests typically go in `_test.go` files and are
// named beginning with `Benchmark`. The `testing` runner
// executes each benchmark function several times, increasing
// `b.N` on each run until it collects a precise measurement.
func BenchmarkIntMin(b *testing.B) {
	// Typically the benchmark runs a function we're
	// benchmarking in a loop `b.N` times.
	for i := 0; i < b.N; i++ {
		IntMin(1, 2)
	}
}

# Run all tests in the current project in verbose mode.
$ go test -v
== RUN   TestIntMinBasic
--- PASS: TestIntMinBasic (0.00s)
=== RUN   TestIntMinTableDriven
=== RUN   TestIntMinTableDriven/0,1
=== RUN   TestIntMinTableDriven/1,0
=== RUN   TestIntMinTableDriven/2,-2
=== RUN   TestIntMinTableDriven/0,-1
=== RUN   TestIntMinTableDriven/-1,0
--- PASS: TestIntMinTableDriven (0.00s)
    --- PASS: TestIntMinTableDriven/0,1 (0.00s)
    --- PASS: TestIntMinTableDriven/1,0 (0.00s)
    --- PASS: TestIntMinTableDriven/2,-2 (0.00s)
    --- PASS: TestIntMinTableDriven/0,-1 (0.00s)
    --- PASS: TestIntMinTableDriven/-1,0 (0.00s)
PASS
ok  	examples/testing-and-benchmarking	0.023s

# Run all benchmarks in the current project. All tests
# are run prior to benchmarks. The `bench` flag filters
# benchmark function names with a regexp.
$ go test -bench=.
goos: darwin
goarch: arm64
pkg: examples/testing
BenchmarkIntMin-8 1000000000 0.3136 ns/op
PASS
ok  	examples/testing-and-benchmarking	0.351s