public void CheckStringTest_NullInput()
{
// Arrange
_nullOrEmptyManager.Setup(x => x.CheckString(It.IsAny <string>())).Returns(true);
// Act
var responseObj = controller.CheckString(null);
var responseModel = responseObj?.Content?.ReadAsAsync <bool>()?.Result;
// Assert
Assert.AreEqual(responseModel, true);
}