@Test
public void singleResolverResolvesPlaceholder() {

    final PipelineFunctionParameterResolverFactory.SingleParameterResolver parameterResolver =
            PipelineFunctionParameterResolverFactory.forStringOrPlaceholderParameter();
    final String params = "(" + KNOWN_PLACEHOLDER + ")";
    when(expressionResolver.resolveAsPipelineElement(anyString()))
            .thenReturn(PipelineElement.resolved(KNOWN_VALUE));
    assertThat(parameterResolver.apply(params, expressionResolver, DUMMY)).contains(KNOWN_VALUE);
    verify(expressionResolver).resolveAsPipelineElement(KNOWN_PLACEHOLDER);
}