StreamWriter.Write() fakable while StreamWriter.WriteLine() unfakable

Isolate.Fake.Instance<System.IO.Stream>(); // Does not throw

Isolate.Fake.Instance<System.IO.TextReader>(); // Does not throw

Isolate.Fake.Instance<System.IO.TextWriter>(); // Does not throw

Isolate.Fake.Instance<System.IO.StreamReader>(); // Does not throw

Isolate.Fake.Instance<System.IO.StreamWriter>(); // Does not throw

Isolate.Fake.Instance<System.Text.RegularExpressions.Match>(); // Does not throw

Isolate.Fake.Instance<System.Threading.Thread>(); // Throws

Isolate.Fake.Instance<System.Text.StringBuilder>(); // Throws

Isolate.Fake.Instance<System.IO.FileInfo>(); // Throws

Isolate.Fake.Instance<System.IO.BinaryReader>(); // Throws

Isolate.Fake.Instance<System.IO.BinaryWriter>(); // Throws

 

According to https://www.typemock.com/mscorlib-types , Isolator supports faking these mscorlib types: DateTime, Environment, File, Directory, FileStream, and X509Certificate.

 

For unlisted-yet-fakable type System.IO.StreamWriter, its behavior when faked is rather interesting in that the fake allows asserting that StreamWriter.Write() was called but disallows by way of NullReferenceException asserting that StreamWriter.WriteLine() was called:

 

 

Edit: Right click "Open image in new tab" in Chrome shows this screenshot in full size.

 

Code in screenshot as text:

 

[TestFixture, Isolated]
public class Tests
{
	[Test]
	public void TestFakabilityOfStreamWriterWrite()
	{
		var fakeStreamWriter = Isolate.Fake.Instance<StreamWriter>(Members.MustBeSpecified);
		Isolate.WhenCalled(() => fakeStreamWriter.Write((string)null)).IgnoreCall();
		//
		fakeStreamWriter.Write("Value"); // Does not throw
		//
		Isolate.Verify.WasCalledWithExactArguments(() => fakeStreamWriter.Write("Value"));
		Assert.AreEqual(1, Isolate.Verify.GetTimesCalled(() => fakeStreamWriter.Write((string)null)));
	}

	[Test]
	public void TestFakabilityOfStreamWriterWriteLine()
	{
		var fakeStreamWriter = Isolate.Fake.Instance<StreamWriter>(Members.MustBeSpecified);
		Isolate.WhenCalled(() => fakeStreamWriter.WriteLine((string)null)).IgnoreCall();
		//
		fakeStreamWriter.WriteLine("Value"); // Throws with NullReferenceException
		//
		Isolate.Verify.WasCalledWithExactArguments(() => fakeStreamWriter.WriteLine("Value"));
		Assert.AreEqual(1, Isolate.Verify.GetTimesCalled(() => fakeStreamWriter.WriteLine((string)null)));
	}
}