@Test
@DisplayName("resolve registered function should pass")
void resolve() {

  when(functionSignature.getFunctionName()).thenReturn(mockFunctionName);
  when(mockfunctionResolver.getFunctionName()).thenReturn(mockFunctionName);
  when(mockfunctionResolver.resolve(functionSignature)).thenReturn(functionExpressionBuilder);
  when(mockMap.containsKey(mockFunctionName)).thenReturn(true);
  when(mockMap.get(mockFunctionName)).thenReturn(mockfunctionResolver);
  BuiltinFunctionRepository repo = new BuiltinFunctionRepository(mockMap);
  repo.register(mockfunctionResolver);
  assertEquals(functionExpressionBuilder, repo.resolve(functionSignature));
}