public SmithyDiffTestSuite addTestCase(SmithyDiffTestCase testCase) {
        cases.add(testCase);
        return this;
    }
Adds a test case to the test suite.

@param testCase Test case to add.
@return Returns the test suite.
smithy-diff/src/main/java/software/amazon/smithy/diff/testrunner/SmithyDiffTestSuite.java