This test in itself is not great.. the way the code is set up right now we can't guarantee that uploadsFinished() will be called during the test, so we can't have the test wait for that to be called. Secondly, since uploadsFinished is run on a separate thread (the UI thread), we might run that callback after we have cleaned up the minidump files we added in the test - and since whether we want to reschedule depends on whether there are any files left to upload, the callback will then tell us that we do not want to reschedule - and subsequently cause a crash on the UI thread..

I think if we want to test this properly we have to make the test wait until the UI thread no longer has any pending tasks to execute. 

This is one reason why the linux_android_rel_ng tryserver is unreliable:
https://ci.chromium.org/buildbot/tryserver.chromium.android/linux_android_rel_ng/456964

Test log:

12-20 21:53:16.809 22850 22864 I TestRunner: started: testCancelFailedUploadCausesReschedule(org.chromium.components.minidump_uploader.MinidumpUploaderImplTest)
12-20 21:53:16.809 22850 22850 I MonitoringInstrumentation: Activities that are still in CREATED to STOPPED: 0
12-20 21:53:16.819 22850 22869 E cr_MinidumpUploaderImpl: Crash directory doesn't exist!
12-20 21:53:16.819 22850 22869 W dalvikvm: threadid=12: thread exiting with uncaught exception (group=0x41599ba8)
12-20 21:53:16.819 22837 22837 D AndroidRuntime: Shutting down org.chromium.chrome.browser.ApplicationLifetime$Observer
12-20 21:53:16.819 22850 22864 I TestRunner: finished: testCancelFailedUploadCausesReschedule(org.chromium.components.minidump_uploader.MinidumpUploaderImplTest)
12-20 21:53:16.819 22850 22854 D dalvikvm: GC_CONCURRENT freed 341K, 3% free 16946K/17320K, paused 2ms+1ms, total 22ms
12-20 21:53:16.819 22837 22844 D dalvikvm: GC_CONCURRENT freed 102K, 16% free 568K/672K, paused 0ms+0ms, total 2ms
12-20 21:53:16.819 22850 22869 E AndroidRuntime: FATAL EXCEPTION: MinidumpUploader-WorkerThread
12-20 21:53:16.819 22850 22869 E AndroidRuntime: Process: org.chromium.chrome, PID: 22850
12-20 21:53:16.819 22850 22869 E AndroidRuntime: java.lang.AssertionError
12-20 21:53:16.819 22850 22869 E AndroidRuntime: 	at org.junit.Assert.fail(Assert.java:86)
12-20 21:53:16.819 22850 22869 E AndroidRuntime: 	at org.junit.Assert.assertTrue(Assert.java:41)
12-20 21:53:16.819 22850 22869 E AndroidRuntime: 	at org.junit.Assert.assertTrue(Assert.java:52)
12-20 21:53:16.819 22850 22869 E AndroidRuntime: 	at org.chromium.components.minidump_uploader.MinidumpUploaderImplTest$8.uploadsFinished(MinidumpUploaderImplTest.java:245)
12-20 21:53:16.819 22850 22869 E AndroidRuntime: 	at org.chromium.components.minidump_uploader.MinidumpUploaderImpl$UploadRunnable.run(MinidumpUploaderImpl.java:95)
12-20 21:53:16.819 22850 22869 E AndroidRuntime: 	at java.lang.Thread.run(Thread.java:841)
12-20 21:53:16.819   780   792 W ActivityManager: Error in app org.chromium.chrome running instrumentation ComponentInfo{org.chromium.chrome.tests/org.chromium.base.test.BaseChromiumAndroidJUnitRunner}:
12-20 21:53:16.819   780   792 W ActivityManager:   java.lang.AssertionError
12-20 21:53:16.819   780   792 W ActivityManager:   java.lang.AssertionError
12-20 21:53:17.039   780   792 I ActivityManager: Force stopping org.chromium.chrome appid=10074 user=0: finished inst
12-20 21:53:17.039   780   792 I ActivityManager: Killing 22850:org.chromium.chrome/u0a74 (adj 0): stop org.chromium.chrome
12-20 21:53:17.159 22876 22876 I test_runner_py: END org.chromium.components.minidump_uploader.MinidumpUploaderImplTest#testCancelFailedUploadCausesReschedule 


Please do something about this test. It's one of the reasons that linux_android_rel_ng is unacceptably flaky.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/915a3e2fdff7985d6dc755e2ce350a930bce6ac1

commit 915a3e2fdff7985d6dc755e2ce350a930bce6ac1
Author: Gustav Sennton <gsennton@google.com>
Date: Fri Dec 22 13:29:16 2017

[Minidump uploader] fix flaky test in MinidumpUploaderImplTest

Fix MinidumpUploaderImplTest#testCancelFailedUploadCausesReschedule by
waiting for the minidump uploads worker thread to finish before ending
the testCancelFailedUploadCausesReschedule test.

BUG= 786310 

Change-Id: I2cd1cde84faf2f44bd69018ed17bbecaa09d6fb8
Reviewed-on: https://chromium-review.googlesource.com/840682
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Gustav Sennton <gsennton@chromium.org>
Cr-Commit-Position: refs/heads/master@{#525982}
[modify] https://crrev.com/915a3e2fdff7985d6dc755e2ce350a930bce6ac1/components/minidump_uploader/android/javatests/src/org/chromium/components/minidump_uploader/MinidumpUploaderImplTest.java