output

λ go test ./...                                                                                                                                          1 ↵ 
--- FAIL: TestRetryAlwaysFailing (1.01s)
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
        retry_test.go:10: I am always failing
FAIL
FAIL    github.com/libkermit/retry      1.309s

retry.go

package retry

import (
	"io"
	"sync"
	"testing"
	"time"
	"unsafe"
)

type _T struct {
	common
	isParallel bool
	context    *testContext // For running tests and subtests.
}

type common struct {
	mu       sync.RWMutex // guards output, failed, and done.
	output   []byte       // Output generated by test or benchmark.
	w        io.Writer    // For flushToParent.
	chatty   bool         // A copy of the chatty flag.
	failed   bool         // Test or benchmark has failed.
	skipped  bool         // Test of benchmark has been skipped.
	finished bool         // Test function has completed.
	done     bool         // Test is finished and all subtests have completed.

	parent   *common
	level    int       // Nesting depth of test or benchmark.
	name     string    // Name of test or benchmark.
	start    time.Time // Time test or benchmark started
	duration time.Duration
	barrier  chan bool    // To signal parallel subtests they may start.
	signal   chan bool    // To signal a test is done.
	sub      []*testing.T // Queue of subtests to be run in parallel.
}

type testContext struct {
	match *matcher

	mu sync.Mutex

	// Channel used to signal tests that are ready to be run in parallel.
	startParallel chan bool

	// running is the number of tests currently running in parallel.
	// This does not include tests that are waiting for subtests to complete.
	running int

	// numWaiting is the number tests waiting to be run in parallel.
	numWaiting int

	// maxParallel is a copy of the parallel flag.
	maxParallel int
}

type matcher struct {
	filter    []string
	matchFunc func(pat, str string) (bool, error)

	mu       sync.Mutex
	subNames map[string]int64
}

func For(t *testing.T, timeout time.Duration, fn func(*testing.T)) {
	ht := (*_T)(unsafe.Pointer(t))
	after := time.After(timeout)
	var timedOut bool
	for {
		fn(t)
		select {
		case <-after:
			timedOut = true
		default:
		}
		if !t.Failed() {
			break
		}
		if !timedOut {
			ht.mu.Lock()
			ht.failed = false
			ht.mu.Unlock()
		}
		if timedOut {
			break
		}
		time.Sleep(100 * time.Millisecond)
	}
}

retry_test.go

package retry

import (
	"testing"
	"time"
)

func TestRetryAlwaysFailing(t *testing.T) {
	For(t, time.Second, func(t *testing.T) {
		t.Error("I am always failing")
	})
}
func TestRetryFailingABit(t *testing.T) {
	i := 0
	For(t, time.Second, func(t *testing.T) {
		if i < 3 {
			t.Error("I am always failing")
		}
		i++
	})
}

func TestRetryAlwaysSucceeding(t *testing.T) {
	For(t, time.Second, func(t *testing.T) {
		// don't do a thing
	})
}