@Test
public void pathsMustBeWithinBaseDir() {

    Exception thrown = Assertions.assertThrows(SmithyBuildException.class, () -> {
        FileManifest a = new MockManifest(Paths.get("/foo"));
        a.addFile(Paths.get("/not/within/parent"));
    });
    assertThat(thrown.getMessage(), containsString("must be relative to the base directory"));
}