Bug 1272431 - Correct order errors in maybePrunePings tests. r=ahunt

MozReview-Commit-ID: CQKjiD5PomF

--HG--
extra : rebase_source : cc06c7ecbf958f3a82cf982fbcc491772b56f63e

mobile/android/base/java/org/mozilla/gecko/telemetry/stores/TelemetryPingStore.java

@@ -37,6 +37,7 @@ public interface TelemetryPingStore extends Parcelable {
 
     /**
      * Removes telemetry pings from the store if there are too many pings or they take up too much space.
+     * Pings should be removed from oldest to newest.
      */
     void maybePrunePings();
 

mobile/android/tests/background/junit4/src/org/mozilla/gecko/telemetry/stores/TestTelemetryJSONFilePingStore.java

@@ -140,16 +140,14 @@ public class TestTelemetryJSONFilePingStore {
     @Test
     public void testMaybePrunePingsPrunesIfAboveMax() throws Exception {
         final int pingCount = TelemetryJSONFilePingStore.MAX_PING_COUNT + 1;
-        writeTestPingsToStore(pingCount, "whatever");
+        final List<String> expectedDocIDs = writeTestPingsToStore(pingCount, "whatever");
         assertStoreFileCount(pingCount);
         testStore.maybePrunePings();
         assertStoreFileCount(TelemetryJSONFilePingStore.MAX_PING_COUNT);
 
         final HashSet<String> existingIDs = new HashSet<>(TelemetryJSONFilePingStore.MAX_PING_COUNT);
-        for (final String filename : testDir.list()) {
-            existingIDs.add(filename);
-        }
-        assertFalse("Smallest ID was removed", existingIDs.contains(1));
+        Collections.addAll(existingIDs, testDir.list());
+        assertFalse("Oldest ping was removed", existingIDs.contains(expectedDocIDs.get(0)));
     }
 
     @Test
@@ -184,16 +182,22 @@ public class TestTelemetryJSONFilePingStore {
      *
      * Note: assumes {@link TelemetryJSONFilePingStore#getPingFile(String)} works.
      *
-     * @return a list of doc IDs saved to disk
+     * @return a list of doc IDs saved to disk in ascending order of last modified date
      */
     private List<String> writeTestPingsToStore(final int count, final String urlPrefix) throws Exception {
         final List<String> savedDocIDs = new ArrayList<>(count);
+        final long now = System.currentTimeMillis();
         for (int i = 1; i <= count; ++i) {
             final String docID = getDocID();
             final JSONObject obj = new JSONObject()
                     .put(TelemetryJSONFilePingStore.KEY_URL_PATH, urlPrefix + docID)
                     .put(TelemetryJSONFilePingStore.KEY_PAYLOAD, generateTelemetryPayload());
-            FileUtils.writeJSONObjectToFile(testStore.getPingFile(docID), obj);
+            final File pingFile = testStore.getPingFile(docID);
+            FileUtils.writeJSONObjectToFile(pingFile, obj);
+
+            // If we don't set an explicit time, the modified times are all equal.
+            // Also, last modified times are rounded by second.
+            assertTrue("Able to set last modified time", pingFile.setLastModified(now - (count * 10_000) + i * 10_000));
             savedDocIDs.add(docID);
         }
         return savedDocIDs;