@Test
public void resolveExpressionInvalid() {

    final FeedMetadata metadata = new FeedMetadata();
    // Verify missing config variable
    final NifiProperty prop1 = createProperty("${config.test.invalid}");
    Assert.assertFalse(resolver.resolveExpression(metadata, prop1));
    Assert.assertEquals("${config.test.invalid}", prop1.getValue());
    // Verify missing metadata variable
    final NifiProperty prop2 = createProperty("${metadata.invalid}");
    Assert.assertFalse(resolver.resolveExpression(metadata, prop2));
    Assert.assertEquals("${metadata.invalid}", prop2.getValue());
    // Verify empty variable
    final NifiProperty prop3 = createProperty("${}");
    Assert.assertFalse(resolver.resolveExpression(metadata, prop3));
    Assert.assertEquals("${}", prop3.getValue());
}