public void Greet()
{
// Arrange
var mock = new Mock <IHelloWorldRepository>();
var expectedResult = "Hello World";
mock.Setup(hello => hello.Greet()).Returns(expectedResult);
HelloWorldController controller = new HelloWorldController(mock.Object);
// Act
var actualResult = controller.Greet();
// Assert
Assert.IsNotNull(actualResult);
Assert.AreEqual(expectedResult, actualResult);
}