function defineTest(dirName, transformName, options, testFilePrefix, testOptions) {
  const testName = testFilePrefix
    ? `transforms correctly using "${testFilePrefix}" data`
    : 'transforms correctly';
  describe(transformName, () => {
    it(testName, () => {
      const testResult = runTest(dirName, transformName, options, testFilePrefix, testOptions);
      return testResult instanceof Promise ? testResult : undefined;
    });
  });
}
Handles some boilerplate around defining a simple jest/Jasmine test for a
jscodeshift transform.