src/main/java/org/fest/assertions/api/AbstractObjectAssert.java
public S isInstanceOf(Class<?> type) {
    objects.assertIsInstanceOf(description, actual, type);
    return myself;
  }
public S isInstanceOf(Class<?> type) {
    objects.assertIsInstanceOf(description, actual, type);
    return myself;
  }
Verifies that the <em>actual</em> value is an instance of the given type.

@param type the type to check the <em>actual</em> value against.
@return this assertion object.
@throws NullPointerException if the given type is {@code null}.
@throws AssertionError if the <em>actual</em> value is {@code null}.
@throws AssertionError if the <em>actual</em> value is not an instance of the given type.