tpl/tplimpl: Simplify some test assertions

htesting/hqt/checkers.go

@@ -96,6 +96,32 @@ func normalizeString(s string) string {
 	return strings.Join(lines, "\n")
 }
 
+// IsAllElementsEqual asserts that all elements in the slice are equal.
+var IsAllElementsEqual qt.Checker = &sliceAllElementsEqualChecker{
+	argNames: []string{"got"},
+}
+
+type sliceAllElementsEqualChecker struct {
+	argNames
+}
+
+func (c *sliceAllElementsEqualChecker) Check(got any, args []any, note func(key string, value any)) (err error) {
+	gotSlice := reflect.ValueOf(got)
+	numElements := gotSlice.Len()
+	if numElements < 2 {
+		return nil
+	}
+	first := gotSlice.Index(0).Interface()
+	// Check that the others are equal to the first.
+	for i := 1; i < numElements; i++ {
+		if diff := cmp.Diff(first, gotSlice.Index(i).Interface()); diff != "" {
+			return fmt.Errorf("element %d is not equal to the first element:\n%s", i, diff)
+		}
+	}
+
+	return nil
+}
+
 // DeepAllowUnexported creates an option to allow compare of unexported types
 // in the given list of types.
 // see https://github.com/google/go-cmp/issues/40#issuecomment-328615283