C# Unit-Tests - Advanced Cheat Sheet

public void Test() {
  // Arrange
  var mock = new Mock<IActionInterface>();
  var subject = new MySubject(mock.Object);
   
  // Act
  subject.DoSomething();
 
  // Assert
  mock.Verify(e => e.Store(It.IsAny<int>()), Times.Once);
}

// If one of these equality comparisons fail we just know that MyAction wasn't called with those arguments.
mock.Verify(e =>  e.MyAction(
  It.Is<ParameterType>(param =>
    param.Field1 == "some value" && 
    param.Field2 == 3),
  Times.Once);

// Instead:
ParameterType calledArgs = null;
mock
  .Setup(e => e.MyAction(It.IsAny<ParameterType>()))
  .Callback<ParameterType>(param => calledArgs = param);

Assert.That(calledArgs, Is.Not.Null);
Assert.That(calledArgs.Field1, Is.EqualTo("some value"));
Assert.That(calledArgs.Field2, Is.EqualTo(3));

private int _someVariable;
 
private MySubject MakeSubject()
{
  var mock = new Mock<IActionInterface>();
 
  mock.Setup(e => e.Action(It.IsAny<int>()))
      .Callback<Int>(s => _someVariable= s);
 
  return new MySubject(mock.Object);
}
 
private bool WasStored(int value) => 
  _someVariable == value;
 
[Test]
public void SomeTestMethod()
{
  // Arrange
  var subject = MakeSubject();
 
  // Act
  subject.DoSomething();
 
  // Assert
  Assert.True(WasStored(5));
}

internal abstract class WebApiTests {
  private WebApplicationFactory<Startup> _factory;{{nl}}
  protected WebApiTests() => 
    _factory = new WebApplicationFactory<Startup>();{{nl}}
  protected HttpClient GetClient() => 
    _factory.CreateClient();
}

class MyApiControllerTests : WebApiTests {

  public async Task requestTest() {
    // Arrange
    var client = GetClient();{{nl}}

    // Act
    var response = await client.GetAsync("api/someuri");{{nl}}

    // Assert
    response.EnsureSuccessStatusCode();
    var data = await response.Content.ReadAsAsync<Model>();{{nl}}

    // Assert data ...
  }
}

// Hide file access through Stream Factory
public interface IStreamFactory
{
  Stream OpenStream();
  void CloseStream(Stream stream);
}

// On test file
private IStreamFactory MakeStreamStorage()
{
  // Create one isolated MemoryStream per test run!
  _stream = new MemoryStream();
  var mock = new Mock<IStreamFactory>();
  mock.Setup(s => s.OpenStream()).Returns(_stream);
  return mock.Object;
}

void Test() {
  // slow & can fail
  var data = File.ReadAllText(@"Data.json");
  // slow & can fail
  var x = JsonConvert.DeserializeObject<MyModel>(data);

  // None of the above lines have anything to do with the test. It's all about Arrange section.
}