@TestWithResources  // <-- add extension
public class InjectTextResourcesTests {

    @GivenTextResource("/com/adelean/junit/jupiter/resource.txt")
    String resourceContent;   // <-- inject resource content

    @Test
    public void testInjectTextIntoStringInstanceField() {
        assertThat(resourceContent)
                .isEqualTo("The quick brown fox jumps over the lazy dog.");
    }
}