NSubstitute

https://github.com/nsubstitute/NSubstitute

 

http://nsubstitute.github.io/help/creating-a-substitute/

NSubstitute完全手册索引 

 

What's the default value will NSubstitute return for a method? example code in C# and NUnit

In NSubstitute, by default, methods will return default values for reference types (e.g. null for string) and default values for value types (e.g. 0 for int). This means that, by default, methods called on a NSubstitute substitute will return the default value for their return type, unless specifically configured to return a different value. Here is an example in C# using NUnit:

[Test]
public void DefaultReturnValues_Example()
{
    // Arrange
    var substitute = Substitute.For<IFoo>();

    // Act
    var result = substitute.Bar();

    // Assert
    Assert.AreEqual(default(int), result);
}

public interface IFoo
{
    int Bar();
}

In this example, IFoo.Bar returns an int, so the default value for int is returned by NSubstitute, which is 0. You can then set up a return value for the method using substitute.Bar().Returns(...) to return a specific value.

 

explain the code

 [Test]
        public void Analyze_LoggerThrows_CallWebServiceWithNSub()
        {
            var mockWebService = Substitute.For<IWebService>();
            var stubLogger = Substitute.For<ILogger>();
            stubLogger.When(logger=>logger.LogError(Arg.Any<string>()))//Simulates exception on any input
                .Do(info => throw new Exception("fake exception"));

            var analyzer = new LogAnalyzer2(stubLogger, mockWebService);
            analyzer.MinNameLength = 10;
            analyzer.Analyze("Short.txt");

            mockWebService.Received()//Checks that mock web service was called with a string containing "fake exception"
                .Write(Arg.Is<string>(s => s.Contains("fake exception")));
        }

 

This is an example of using NSubstitute to write a test for a class named LogAnalyzer2. The test method Analyze_LoggerThrows_CallWebServiceWithNSub is testing the behavior of LogAnalyzer2 when a logger throws an exception.

The code sets up a mock implementation of the IWebService interface using Substitute.For<IWebService>(), and a stub implementation of the ILogger interface using Substitute.For<ILogger>().

The stub implementation of ILogger is then set up to throw an exception with the message "fake exception" whenever its LogError method is called with any argument, by using When(logger=>logger.LogError(Arg.Any<string>())) and Do(info => throw new Exception("fake exception")).

An instance of LogAnalyzer2 is then created, passing the stub logger and mock web service as arguments. The test sets the MinNameLength property to 10, and calls the Analyze method with the argument "Short.txt".

The final line of the test uses mockWebService.Received() and Write(Arg.Is<string>(s => s.Contains("fake exception"))) to verify that the mock web service's Write method was called with a string that contains the message "fake exception". This verifies that when the Logger throws an exception, the LogAnalyzer2 class calls the Write method on the web service with the error message.