Telerik JustMock
[TestMethod]
public void ShouldMockInstanceCallPartially()
{
// Arrange
Foo foo = new Foo();
// Just a single method of the original object is mocked.
Mock.Arrange(() => foo.Echo(Arg.IsAny<int>())).Returns((int arg) => arg);
// Act
int actual = foo.Echo(10);
// Assert
Assert.AreEqual(10, actual);
}