例子

下面这个例子中使用了TemporaryFolder和ExpectedException规则:

    public class DigitalAssetManagerTest {
      @Rule
      public TemporaryFolder tempFolder = new TemporaryFolder();

      @Rule
      public ExpectedException exception = ExpectedException.none();

      @Test
      public void countsAssets() throws IOException {
        File icon = tempFolder.newFile("icon.png");
        File assets = tempFolder.newFolder("assets");
        createAssets(assets, 3);

        DigitalAssetManager dam = new DigitalAssetManager(icon, assets);
        assertEquals(3, dam.getAssetCount());
      }

      private void createAssets(File assets, int numberOfAssets) throws IOException {
        for (int index = 0; index < numberOfAssets; index++) {
          File asset = new File(assets, String.format("asset-%d.mpg", index));
          Assert.assertTrue("Asset couldn't be created.", asset.createNewFile());
        }
      }

      @Test
      public void throwsIllegalArgumentExceptionIfIconIsNull() {
        exception.expect(IllegalArgumentException.class);
        exception.expectMessage("Icon is null, not a file, or doesn't exist.");
        new DigitalAssetManager(null, null);
      }
    }

JUnit提供的一些基本rule

请看下面的内容