Add more common errors to JUnit4 documentation

testing/android/docs/junit4.md

Index: testing/android/docs/junit4.md
diff --git a/testing/android/docs/junit4.md b/testing/android/docs/junit4.md
index d40583fbe545490aef7c961bb61fb5b9526bc905..fbf31af0f83c5a2c22fcbc8efbe22e9bd983551f 100644
--- a/testing/android/docs/junit4.md
+++ b/testing/android/docs/junit4.md
@@ -146,24 +146,27 @@ public class MyRule implements TestRule {
 ```
 
 
-## Caveats
+## Common Errors
 
 1.  Instrumentation tests that rely on test thread to have message handler
     will not work. For example error message:
 
         java.lang.RuntimeException: Can't create handler inside thread that has not called Looper.prepare()
 
-    Please utilize `@UiThreadTest` or
-    `ActivityTestRule.runOnUiThread(Runnable r)` to refactor these tests.
-    For more, check this [GitHub issue][6]
-
-1.  Use `@UiThreadTest` with caution. Currently,
-    **@UiThreadTest is only effective when UiThreadTestRule or
-    ActivityTestRule is declared** in the test class. Please use
-    `android.support.test.annotation.UiThreadTest`, not
-    `android.test.UiThreadTest`. When using @UiThreadTest, **it would cause
-    `setUp` and `tearDown` to run in Ui Thread** as well. Avoid that by simply
-    calling [`runOnUiThread`][9] or [`runOnMainSync`][10] with a Runnable.
+    or
+        java.lang.IllegalStateException: The current thread must have a looper!

[jbudorick, 2017/05/04 19:40:47]

I think you need an extra blank line before this one.

[the real yoland, 2017/05/04 19:53:28]

Done

+
+    Please utilize `ActivityTestRule.runOnUiThread(Runnable r)` to refactor
+    these tests. For more, check this [GitHub issue][6]
+
+1.  Use `@UiThreadTest` with caution!!
+    -   Currently, **@UiThreadTest is only effective when UiThreadTestRule or
+        ActivityTestRule is declared** in the test class.
+    -   Please use **`android.support.test.annotation.UiThreadTest`, NOT
+        `android.test.UiThreadTest`**.
+    -   When using @UiThreadTest, **it would cause `setUp` and `tearDown` to
+        run in Ui Thread** as well. Avoid that by calling [`runOnUiThread`][9]
+        or [`runOnMainSync`][10] with a Runnable.
     
     ```java
     // Wrong test
@@ -218,6 +221,11 @@ public class MyRule implements TestRule {
     `Assert.assertEquals(float a, float b, float delta)`
 
 
+1.  Error-prone warning when disabling a javatest in JUnit4. If you get a

[jbudorick, 2017/05/04 19:40:47]

Rephrase:

 1. Errorprone expects all methods starting with `test...` to be annotated with
`@Test`. Failure to meet that expectation will cause errorprone to fail with
something like this:

  `[JUnit4TestNotRun] ...`

  In particular, you may see this when attempting to disable tests. In that
case, the test should be annotated with both @DisabledTest and @Test.

[the real yoland, 2017/05/04 19:53:28]

Done

+    `[JUnit4TestNotRun] Test method will not be run; please add @Test annotation`
+    warning. It's likely because you commented out `@Test` when adding
+    `@DisabledTest` or `@FlakyTest`.
+
 ## Common questions
 
 -   Q: Are `@Test` and `@LargeTest/@MediumTest/@SmallTest` annotation both