pkg/testutils: utility functions to facilitate writing Go tests

Docker-DCO-1.1-Signed-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)

testutils/MAINTAINERS

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+Solomon Hykes <s@docker.com> (@shykes)

testutils/README.md

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+`testutils` is a collection of utility functions to facilitate the writing
+of tests. It is used in various places by the Docker test suite.

testutils/testutils.go

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+package testutils
+
+import (
+	"testing"
+	"time"
+)
+
+// Timeout calls f and waits for 100ms for it to complete.
+// If it doesn't, it causes the tests to fail.
+// t must be a valid testing context.
+func Timeout(t *testing.T, f func()) {
+	onTimeout := time.After(100 * time.Millisecond)
+	onDone := make(chan bool)
+	go func() {
+		f()
+		close(onDone)
+	}()
+	select {
+	case <-onTimeout:
+		t.Fatalf("timeout")
+	case <-onDone:
+	}
+}