improved delivery tests

delivery_test.go

@@ -12,18 +12,18 @@ func TestSequentialDelivery(t *testing.T) {
 	feedback := make([]int, 0, 3)
 
 	subscribers := []Subscriber[int]{
-		func(i int) bool {
-			assert.Equalf(t, testMsg, i, "expected %d but got %d", testMsg, i)
+		func(msg int) bool {
+			assert.Equalf(t, testMsg, msg, "expected %d but got %d", testMsg, msg)
 			feedback = append(feedback, 1)
-			return true
-		},
-		func(i int) bool {
-			assert.Equalf(t, testMsg, i, "expected %d but got %d", testMsg, i)
-			feedback = append(feedback, 2)
 			return false
 		},
-		func(i int) bool {
-			assert.Equalf(t, testMsg, i, "expected %d but got %d", testMsg, i)
+		func(msg int) bool {
+			assert.Equalf(t, testMsg, msg, "expected %d but got %d", testMsg, msg)
+			feedback = append(feedback, 2)
+			return true
+		},
+		func(msg int) bool {
+			assert.Equalf(t, testMsg, msg, "expected %d but got %d", testMsg, msg)
 			feedback = append(feedback, 3)
 			return true
 		},
@@ -38,4 +38,25 @@ func TestSequentialDelivery(t *testing.T) {
 
 	assert.Len(t, finalSubscribers, len(nextSubscribers), "expected to have the same subscribers")
 	assert.Len(t, feedback, 5, "one or more subscriber was not called")
+
+	assertContainsExactlyN(t, 1, 1, feedback)
+	assertContainsExactlyN(t, 2, 2, feedback)
+	assertContainsExactlyN(t, 3, 2, feedback)
+}
+
+func assertContainsExactlyN[T comparable](t testing.TB, exp T, n int, slice []T) {
+	t.Helper()
+
+	var found int
+	for _, v := range slice {
+		if exp == v {
+			found++
+		}
+	}
+
+	if n > found {
+		t.Errorf("contains too few '%v': expected %d but found %d", exp, n, found)
+	} else if n < found {
+		t.Errorf("contains too many '%v': expected %d but found %d", exp, n, found)
+	}
 }