@Override
        public String toString() {
            StringBuilder builder = new StringBuilder();

            builder
                    .append("============================\n"
                            + "Model Diff Validation Result\n"
                            + "============================\n")
                    .append(name)
                    .append('\n');

            if (!unmatchedEvents.isEmpty()) {
                builder.append("\nDid not match the following events\n"
                        + "----------------------------------\n");
                for (ValidationEvent event : unmatchedEvents) {
                    builder.append(event.toString()).append("\n\n");
                }
            }

            if (!extraEvents.isEmpty()) {
                builder.append("\nEncountered unexpected events\n"
                        + "-----------------------------\n");
                for (ValidationEvent event : extraEvents) {
                    builder.append(event.toString()).append("\n\n");
                }
            }

            return builder.toString();
        }
Output of diffing a model against a test case.
smithy-diff/src/main/java/software/amazon/smithy/diff/testrunner/SmithyDiffTestCase.java