1.测试例子分析
example_test.go,展示了With-系列的4个例子
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func ExampleWithCancel() { gen := func(ctx context.Context) <-chan int { dst := make(chan int) n := 1 go func() { for { select { case <-ctx.Done(): return // returning not to leak the goroutine case dst <- n: n++ } } }() return dst } ctx, cancel := context.WithCancel(context.Background()) defer cancel() // cancel when we are finished consuming integers for n := range gen(ctx) { fmt.Println(n) if n == 5 { break } } // Output: // 1 // 2 // 3 // 4 // 5} |
结构分析,gen是一个函数,返回值是一个信道, for range channel是有特殊意义的, for会循环从channel读数据,直到channel被close(),不然就是无限循环.
gen内部的协程就是典型的闭包,for range会不断触发读,gen内部的for select 会不断触发写,主协程读5次之后,会结束main函数,会触发defer函数, 也就是取消操作对应的回调,此时done信道会被close,gen内部的协程会正常退出.
这个例子是测试支持取消信号的上下文,取消函数的调用放在了main的defer函数中.
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const shortDuration = 1 * time.Millisecondfunc ExampleWithDeadline() { d := time.Now().Add(shortDuration) ctx, cancel := context.WithDeadline(context.Background(), d) // Even though ctx will be expired, it is good practice to call its // cancellation function in any case. Failure to do so may keep the // context and its parent alive longer than necessary. defer cancel() select { case <-time.After(1 * time.Second): fmt.Println("overslept") case <-ctx.Done(): fmt.Println(ctx.Err()) } // Output: // context deadline exceeded} |
deadline的这个例子,在main的defer中也有主动调用取消函数的. 实际上通过打印可以显示deadline是否按预期工作.
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func ExampleWithTimeout() { ctx, cancel := context.WithTimeout(context.Background(), shortDuration) defer cancel() select { case <-time.After(1 * time.Second): fmt.Println("overslept") case <-ctx.Done(): fmt.Println(ctx.Err()) // prints "context deadline exceeded" } // Output: // context deadline exceeded} |
timeout只是deadline的一种简写.
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func ExampleWithValue() { type favContextKey string f := func(ctx context.Context, k favContextKey) { if v := ctx.Value(k); v != nil { fmt.Println("found value:", v) return } fmt.Println("key not found:", k) } k := favContextKey("language") ctx := context.WithValue(context.Background(), k, "Go") f(ctx, k) f(ctx, favContextKey("color")) // Output: // found value: Go // key not found: color} |
context.WithValue和Context.Value()是存取操作, 取的时候,如果key没找到,会返回nil.
2.单元测试
context_text.go,x_test.go是单元测试, example_test.go是示例,benchmark_test.go是基准测试, net_test.go展示了deadline对net包的支持.
先看单元测试的context_text.go.
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type testingT interface {}type otherContext struct {}func quiescent(t testingT) time.Duration {}func XTestBackground(t testingT) {}func XTestTODO(t testingT) {}func XTestWithCancel(t testingT) {}func contains(m map[canceler]struct{}, key canceler) bool {}func XTestParentFinishesChild(t testingT) {}func XTestChildFinishesFirst(t testingT) {}func testDeadline(c Context, name string, t testingT) {}func XTestDeadline(t testingT) {}func XTestTimeout(t testingT) {}func XTestCanceledTimeout(t testingT) {}func XTestValues(t testingT) {}func XTestAllocs(t testingT, testingShort func() bool, testingAllocsPerRun func(int, func()) float64) {}func XTestSimultaneousCancels(t testingT) {}func XTestInterlockedCancels(t testingT) {}func XTestLayersCancel(t testingT) {}func XTestLayersTimeout(t testingT) {}func XTestCancelRemoves(t testingT) {}func XTestWithCancelCanceledParent(t testingT) {}func XTestWithValueChecksKey(t testingT) {}func XTestInvalidDerivedFail(t testingT) {}func recoveredValue(fn func()) (v interface{}) {}func XTestDeadlineExceededSupportsTimeout(t testingT) {}type myCtx struct {}type myDoneCtx struct {}func (d *myDoneCtx) Done() <-chan struct{} {}func XTestCustomContextGoroutines(t testingT) {} |
这暴露的大多测试函数的参数类型是testingT接口类型,但这个源文件中没有实现testingT接口的,
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func TestBackground(t *testing.T) { XTestBackground(t) }func TestTODO(t *testing.T) { XTestTODO(t) }func TestWithCancel(t *testing.T) { XTestWithCancel(t) }func TestParentFinishesChild(t *testing.T) { XTestParentFinishesChild(t) }func TestChildFinishesFirst(t *testing.T) { XTestChildFinishesFirst(t) }func TestDeadline(t *testing.T) { XTestDeadline(t) }func TestTimeout(t *testing.T) { XTestTimeout(t) }func TestCanceledTimeout(t *testing.T) { XTestCanceledTimeout(t) }func TestValues(t *testing.T) { XTestValues(t) }func TestAllocs(t *testing.T) { XTestAllocs(t, testing.Short, testing.AllocsPerRun) }func TestSimultaneousCancels(t *testing.T) { XTestSimultaneousCancels(t) }func TestInterlockedCancels(t *testing.T) { XTestInterlockedCancels(t) }func TestLayersCancel(t *testing.T) { XTestLayersCancel(t) }func TestLayersTimeout(t *testing.T) { XTestLayersTimeout(t) }func TestCancelRemoves(t *testing.T) { XTestCancelRemoves(t) }func TestWithCancelCanceledParent(t *testing.T) { XTestWithCancelCanceledParent(t) }func TestWithValueChecksKey(t *testing.T) { XTestWithValueChecksKey(t) }func TestInvalidDerivedFail(t *testing.T) { XTestInvalidDerivedFail(t) }func TestDeadlineExceededSupportsTimeout(t *testing.T) { XTestDeadlineExceededSupportsTimeout(t) }func TestCustomContextGoroutines(t *testing.T) { XTestCustomContextGoroutines(t) } |
这是x_test.go的内容,直接是用testing.T类型来实现testingT接口.
那先分析一下testing.T对testingT接口的实现.
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type T struct { common isParallel bool context *testContext}func (t *T) Deadline() (deadline time.Time, ok bool) { deadline = t.context.deadline return deadline, !deadline.IsZero()} |
注意：testing.T.context不是context.Context的实现类型, Deadline()返回了t.context中存储的deadline信息.
testing.T内嵌了testing.common,大部分方法集都来至common:
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Error(args ...interface{})Errorf(format string, args ...interface{})Fail()FailNow()Failed() boolFatal(args ...interface{})Fatalf(format string, args ...interface{})Helper()Log(args ...interface{})Logf(format string, args ...interface{})Name() stringSkip(args ...interface{})SkipNow()Skipf(format string, args ...interface{})Skipped() bool |
Parallel()是由testing.T实现,某个测试用例多次重复执行时, 可启用并发参数.
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原文链接：https://juejin.cn/post/7062246261667135518
