src/main/java/org/fest/assertions/internal/Objects.java
public void assertIsNotInstanceOf(Description description, Object actual, Class<?> type) {
    checkNotNull(type);
    if (type.isInstance(actual)) {
      String format = "expecting <%s> not to be an instance of:<%s>";
      throw failures.failure(description, new BasicErrorMessageFactory(format, actual, type));
    }
  }
public void assertIsNotInstanceOf(Description description, Object actual, Class<?> type) {
    checkNotNull(type);
    if (type.isInstance(actual)) {
      String format = "expecting <%s> not to be an instance of:<%s>";
      throw failures.failure(description, new BasicErrorMessageFactory(format, actual, type));
    }
  }
Asserts that the <em>actual</em> object is not an instance of the given type.

@param description the description of the <em>actual</em> object.
@param actual the <em>actual</em> object.
@param type the type to check the <em>actual</em> object against.
@throws NullPointerException if the given type is {@code null}.
@throws AssertionError if the <em>actual</em> object is an instance of the given type.