public IsJson(Matcher<? super ReadContext> jsonMatcher) {
        this.jsonMatcher = jsonMatcher;
    }
@Test
    public void shouldDescribeMismatchOfValidJson() {
        Matcher<Object> matcher = isJson(withPathEvaluatedTo(true));
        Description description = new StringDescription();
        matcher.describeMismatch(BOOKS_JSON_STRING, description);
        assertThat(description.toString(), containsString(TestingMatchers.MISMATCHED_TEXT));
    }