fix: make assert.CollectT concurrency safe

assert/assertions.go

@@ -1912,8 +1912,8 @@ func EventuallyWithT(t TestingT, condition func(collect *CollectT), waitFor time
 		h.Helper()
 	}
 
-	collect := new(CollectT)
-	ch := make(chan bool, 1)
+	var lastTickErrs []error
+	ch := make(chan []error, 1)
 
 	timer := time.NewTimer(waitFor)
 	defer timer.Stop()
@@ -1924,19 +1924,23 @@ func EventuallyWithT(t TestingT, condition func(collect *CollectT), waitFor time
 	for tick := ticker.C; ; {
 		select {
 		case <-timer.C:
-			collect.Copy(t)
+			for _, err := range lastTickErrs {
+				t.Errorf("%v", err)
+			}
 			return Fail(t, "Condition never satisfied", msgAndArgs...)
 		case <-tick:
 			tick = nil
-			collect.Reset()
 			go func() {
+				collect := new(CollectT)
 				condition(collect)
-				ch <- len(collect.errors) == 0
+				ch <- collect.errors
 			}()
-		case v := <-ch:
-			if v {
+		case errs := <-ch:
+			if len(errs) == 0 {
 				return true
 			}
+			// Keep the last tick's errors, so that they can be copied to t if the condition is not met on time.
+			lastTickErrs = errs
 			tick = ticker.C
 		}
 	}

assert/assertions_test.go

@@ -2786,6 +2786,18 @@ func TestEventuallyWithTTrue(t *testing.T) {
 	Len(t, mockT.errors, 0)
 }
 
+func TestEventuallyWithT_ConcurrencySafe(t *testing.T) {
+	mockT := new(CollectT)
+
+	condition := func(collect *CollectT) {
+		True(collect, false)
+	}
+
+	// To trigger race conditions, we run EventuallyWithT with a nanosecond tick.
+	False(t, EventuallyWithT(mockT, condition, 100*time.Millisecond, time.Nanosecond))
+	Len(t, mockT.errors, 2)
+}
+
 func TestNeverFalse(t *testing.T) {
 	condition := func() bool {
 		return false