Test with NO expected exception

Using NUnit 3.0 Constraint Model type assertions the code would look as follows:

Assert.That(() => SomeMethod(actual), Throws.Nothing);

This example is taken from NUnit wiki.

Assert.DoesNotThrow(() => { /* custom code block here*/});

OR just method

Assert.DoesNotThrow(() => CallMymethod());

For more details see NUnit Exception Asserts