testing

Documentation

Overview

Package testing provides support for automated testing of Go packages. It is intended to be used in concert with the “go test” command, which automates execution of any function of the form

func TestXxx(*testing.T)

where Xxx can be any alphanumeric string (but the first letter must not be in [a-z]) and serves to identify the test routine. These TestXxx routines should be declared within the package they are testing.

Functions of the form

func BenchmarkXxx(*testing.B)

are considered benchmarks, and are executed by the "go test" command when the -test.bench flag is provided.

A sample benchmark function looks like this:

func BenchmarkHello(b *testing.B) {
    for i := 0; i < b.N; i++ {
        fmt.Sprintf("hello")
    }
}

The benchmark package will vary b.N until the benchmark function lasts long enough to be timed reliably. The output

testing.BenchmarkHello    10000000    282 ns/op

means that the loop ran 10000000 times at a speed of 282 ns per loop.

If a benchmark needs some expensive setup before running, the timer may be stopped:

func BenchmarkBigLen(b *testing.B) {
    b.StopTimer()
    big := NewBig()
    b.StartTimer()
    for i := 0; i < b.N; i++ {
        big.Len()
    }
}

The package also runs and verifies example code. Example functions may include a concluding comment that begins with "Output:" and is compared with the standard output of the function when the tests are run, as in these examples of an example:

func ExampleHello() {
        fmt.Println("hello")
        // Output: hello
}

func ExampleSalutations() {
        fmt.Println("hello, and")
        fmt.Println("goodbye")
        // Output:
        // hello, and
        // goodbye
}

Example functions without output comments are compiled but not executed.

The naming convention to declare examples for a function F, a type T and method M on type T are:

func ExampleF() { ... }
func ExampleT() { ... }
func ExampleT_M() { ... }

Multiple example functions for a type/function/method may be provided by appending a distinct suffix to the name. The suffix must start with a lower-case letter.

func ExampleF_suffix() { ... }
func ExampleT_suffix() { ... }
func ExampleT_M_suffix() { ... }

The entire test file is presented as the example when it contains a single example function, at least one other function, type, variable, or constant declaration, and no test or benchmark functions.

Index

• func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, ...)
• func RunBenchmarks(matchString func(pat, str string) (bool, error), ...)
• func RunExamples(matchString func(pat, str string) (bool, error), examples []InternalExample) (ok bool)
• func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool)
• func Short() bool
• type B
  • func (b *B) ResetTimer()
  • func (b *B) SetBytes(n int64)
  • func (b *B) StartTimer()
  • func (b *B) StopTimer()
• type BenchmarkResult
  • func Benchmark(f func(b *B)) BenchmarkResult
  • func (r BenchmarkResult) NsPerOp() int64
  • func (r BenchmarkResult) String() string
• type InternalBenchmark
• type InternalExample
• type InternalTest
• type T
  • func (t *T) Parallel()

Functions

func Main

func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample)

An internal function but exported because it is cross-package; part of the implementation of the "go test" command.

func RunBenchmarks

func RunBenchmarks(matchString func(pat, str string) (bool, error), benchmarks []InternalBenchmark)

An internal function but exported because it is cross-package; part of the implementation of the "go test" command.

func RunExamples

func RunExamples(matchString func(pat, str string) (bool, error), examples []InternalExample) (ok bool)

func RunTests

func RunTests(matchString func(pat, str string) (bool, error), tests []InternalTest) (ok bool)

func Short

func Short() bool

Short reports whether the -test.short flag is set.

Types

type B

type B struct {
	N int
	// contains filtered or unexported fields
}

B is a type passed to Benchmark functions to manage benchmark timing and to specify the number of iterations to run.

func (*B) ResetTimer

func (b *B) ResetTimer()

ResetTimer sets the elapsed benchmark time to zero. It does not affect whether the timer is running.

func (*B) SetBytes

func (b *B) SetBytes(n int64)

SetBytes records the number of bytes processed in a single operation. If this is called, the benchmark will report ns/op and MB/s.

func (*B) StartTimer

func (b *B) StartTimer()

StartTimer starts timing a test. This function is called automatically before a benchmark starts, but it can also used to resume timing after a call to StopTimer.

func (*B) StopTimer

func (b *B) StopTimer()

StopTimer stops timing a test. This can be used to pause the timer while performing complex initialization that you don't want to measure.

type BenchmarkResult

type BenchmarkResult struct {
	N     int
	T     time.Duration
	Bytes int64
}

The results of a benchmark run.

func Benchmark

func Benchmark(f func(b *B)) BenchmarkResult

Benchmark benchmarks a single function. Useful for creating custom benchmarks that do not use the "go test" command.

func (BenchmarkResult) NsPerOp

func (r BenchmarkResult) NsPerOp() int64

func (BenchmarkResult) String

func (r BenchmarkResult) String() string

type InternalBenchmark

type InternalBenchmark struct {
	Name string
	F    func(b *B)
}

An internal type but exported because it is cross-package; part of the implementation of the "go test" command.

type InternalExample

type InternalExample struct {
	Name   string
	F      func()
	Output string
}

type InternalTest

type InternalTest struct {
	Name string
	F    func(*T)
}

An internal type but exported because it is cross-package; part of the implementation of the "go test" command.

type T

type T struct {
	// contains filtered or unexported fields
}

T is a type passed to Test functions to manage test state and support formatted test logs. Logs are accumulated during execution and dumped to standard error when done.

func (*T) Parallel

func (t *T) Parallel()

Parallel signals that this test is to be run in parallel with (and only with) other parallel tests in this CPU group.