diff -r 000000000000 -r 6474c204b198 mobile/android/tests/background/junit3/src/common/TestDateUtils.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/tests/background/junit3/src/common/TestDateUtils.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,83 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+package org.mozilla.gecko.background.common;
+
+import java.text.SimpleDateFormat;
+import java.util.Locale;
+import java.util.TimeZone;
+
+import junit.framework.TestCase;
+
+import org.mozilla.gecko.background.common.DateUtils.DateFormatter;
+//import android.util.SparseArray;
+
+public class TestDateUtils extends TestCase {
+  // Our old, correct implementation -- used to test the new one.
+  public static String getDateStringUsingFormatter(long time) {
+    final SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd", Locale.US);
+    format.setTimeZone(TimeZone.getTimeZone("UTC"));
+    return format.format(time);
+  }
+
+  private void checkDateString(long time) {
+    assertEquals(getDateStringUsingFormatter(time),
+                 new DateUtils.DateFormatter().getDateString(time));
+  }
+
+  public void testDateImplementations() {
+    checkDateString(1L);
+    checkDateString(System.currentTimeMillis());
+    checkDateString(1379118065844L);
+    checkDateString(1379110000000L);
+    for (long i = 0L; i < (2 * GlobalConstants.MILLISECONDS_PER_DAY); i += 11000) {
+      checkDateString(i);
+    }
+  }
+
+  @SuppressWarnings("static-method")
+  public void testReuse() {
+    DateFormatter formatter = new DateFormatter();
+    long time = System.currentTimeMillis();
+    assertEquals(formatter.getDateString(time), formatter.getDateString(time));
+  }
+
+  // Perf tests. Disabled until you need them.
+  /*
+  @SuppressWarnings("static-method")
+  public void testDateTiming() {
+    long start = 1379118000000L;
+    long end   = 1379118045844L;
+
+    long t0 = android.os.SystemClock.elapsedRealtime();
+    for (long i = start; i < end; ++i) {
+      DateUtils.getDateString(i);
+    }
+    long t1 = android.os.SystemClock.elapsedRealtime();
+    System.err.println("CALENDAR: " + (t1 - t0));
+
+
+    t0 = android.os.SystemClock.elapsedRealtime();
+    for (long i = start; i < end; ++i) {
+      getDateStringFormatter(i);
+    }
+    t1 = android.os.SystemClock.elapsedRealtime();
+    System.err.println("FORMATTER: " + (t1 - t0));
+  }
+
+  @SuppressWarnings("static-method")
+  public void testDayTiming() {
+    long start = 33 * 365;
+    long end   = start + 90;
+    int reps   = 1;
+    long t0 = android.os.SystemClock.elapsedRealtime();
+    for (long i = start; i < end; ++i) {
+      for (int j = 0; j < reps; ++j) {
+        DateUtils.getDateStringForDay(i);
+      }
+    }
+    long t1 = android.os.SystemClock.elapsedRealtime();
+    System.err.println("Non-memo: " + (t1 - t0));
+  }
+  */
+}