[FLINK-13934][rest] Use hamcrest for checking String contents

flink-runtime-web/src/test/java/org/apache/flink/runtime/webmonitor/history/HistoryServerStaticFileServerHandlerTest.java

@@ -63,7 +63,7 @@ public void testRespondWithFile() throws Exception {
  // verify that a) a file can be loaded using the ClassLoader and b) that the HistoryServer
  // index_hs.html is injected
  String index = HistoryServerTest.getFromHTTP("http:https://localhost:" + port + "/index.html");
- Assert.assertTrue(index.contains("Apache Flink Web Dashboard"));
+ Assert.assertThat(index, containsString("Apache Flink Web Dashboard"));
 
  // verify that index.html is appended if the request path ends on '/'
  String index2 = HistoryServerTest.getFromHTTP("http:https://localhost:" + port + "/");
@@ -73,12 +73,12 @@ public void testRespondWithFile() throws Exception {
  File dir = new File(webDir, "dir.json");
  dir.mkdirs();
  String dirNotFound404 = HistoryServerTest.getFromHTTP("http:https://localhost:" + port + "/dir");
- Assert.assertTrue(dirNotFound404.contains("not found"));
+ Assert.assertThat(dirNotFound404, containsString("not found"));
 
  // verify that a 404 message is returned when requesting a file outside the webDir
  tmp.newFile("secret");
  String x = HistoryServerTest.getFromHTTP("http:https://localhost:" + port + "/../secret");
- Assert.assertTrue(x.contains("not found"));
+ Assert.assertThat(x, containsString("not found"));
  } finally {
  webUI.shutdown();
  }