Add a ContainsItem func (#8)

assert.go

@@ -113,6 +113,21 @@ func Contains(t testing.TB, haystack string, needle string, msgAndArgs ...any) {
 	t.Fatalf("%s\nNeedle: %q\nHaystack: %q\n", msg, needle, haystack)
 }
 
+// ContainsItem asserts that "haystack" contains "needle".
+func ContainsItem[T any](t testing.TB, haystack []T, needle T, msgAndArgs ...interface{}) {
+	t.Helper()
+	for _, item := range haystack {
+		if objectsAreEqual(item, needle) {
+			return
+		}
+	}
+
+	msg := formatMsgAndArgs("Haystack does not contain needle.", msgAndArgs...)
+	needleRepr := repr.String(needle, repr.Indent("  "))
+	haystackRepr := repr.String(haystack, repr.Indent("  "))
+	t.Fatalf("%s\nNeedle: %s\nHaystack: %s\n", msg, needleRepr, haystackRepr)
+}
+
 // NotContains asserts that "haystack" does not contain "needle".
 func NotContains(t testing.TB, haystack string, needle string, msgAndArgs ...any) {
 	if !strings.Contains(haystack, needle) {

assert_test.go

@@ -65,6 +65,15 @@ func TestContains(t *testing.T) {
 	})
 }
 
+func TestContainsItem(t *testing.T) {
+	assertOk(t, "Found", func(t testing.TB) {
+		ContainsItem(t, []string{"hello", "world"}, "hello")
+	})
+	assertFail(t, "NotFound", func(t testing.TB) {
+		ContainsItem(t, []string{"hello", "world"}, "goodbye")
+	})
+}
+
 func TestNotContains(t *testing.T) {
 	assertOk(t, "NotFound", func(t testing.TB) {
 		NotContains(t, "a haystack with a needle in it", "screw")