how can I create a method in a new class with the SDK

I try to create a new class (it works) but this class doesn't have the created method

The following sourcecode for creating the method doesn't work (the class is created without any method)

private void addTestMethod() {
   final PsiElementFactory elementFactory = ...
   final PsiMethod testMethod = this.factory.createMethod("...", PsiType.VOID);
   testMethod.getBody().add(elementFactory.createExpressionFromText("this.verify()", testMethod));
   this.testClass.add(testMethod);
}