A prototype of a Go implementation of Hamcrest style matchers

hamcrest.go

/*
hamcrest implements very basic hamcrest style asserts
for example:
	func TestStuff(t *testing.T) {
		Assert(t).That(2 * 4, Equals(6))
	}
*/
package hamcrest

import "fmt"
import "reflect"
import "runtime"
import "strings"

type testing interface {
	Error(err ...interface{})
}

type Asserter struct {
	t testing
}

func Assert(t testing) Asserter {
	return Asserter{t}
}

type tester func(interface{}) string

func (a Asserter) That(actual interface{}, test tester) {
	err := test(actual)
	if err != "" {
		a.Fail(err)
	}
}

func (a Asserter) Fail(err string) {
	file, line := getLocation()
	a.t.Error(err + fmt.Sprintf(" {%s:%d}", file, line))
}

func getLocation() (file string, line int) {
	i := 1
	for ; i < 9; i++ {
		_, file, _, ok := runtime.Caller(i)
		if !ok || strings.Contains(file, "testing/testing.go") {
			break
		}
	}
	_, file, line, ok := runtime.Caller(i - 1)
	if ok && i > 1 && i < 9 {
		// Truncate file name at last file name separator.
		if index := strings.LastIndex(file, "/"); index >= 0 {
			file = file[index+1:]
		} else if index = strings.LastIndex(file, "\\"); index >= 0 {
			file = file[index+1:]
		}
	} else {
		file = "???"
		line = 1
	}
	return file, line
}

// Equals checks that the actual value is equal to the expected value
// using reflect.DeepEquals
func Equals(expected interface{}) tester {
	return func(actual interface{}) string {
		if reflect.DeepEqual(expected, actual) {
			return ""
		}
		return fmt.Sprintf("expected %v but got %v", expected, actual)
	}
}

// Comment decorates a tester to add extra text to error messages
func (test tester) Comment(comment string) tester {
	return func(actual interface{}) string {
		err := test(actual)
		if err == "" {
			return ""
		} else {
			return err + " (" + comment + ")"
		}
	}
}