diff --git a/luni/src/test/java/libcore/java/text/DateFormatTest.java b/luni/src/test/java/libcore/java/text/DateFormatTest.java
new file mode 100644
index 0000000..8e215ab
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+++ b/luni/src/test/java/libcore/java/text/DateFormatTest.java
@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package libcore.java.text;
+
+import junit.framework.TestCase;
+
+import java.text.DateFormat;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.Locale;
+
+public class DateFormatTest extends TestCase {
+
+    // Regression test for http://b/31762542. If this test fails it implies that changes to
+    // DateFormat.is24Hour will not be effective.
+    public void testIs24Hour_notCached() throws Exception {
+        Boolean originalIs24Hour = DateFormat.is24Hour;
+        try {
+            // These tests hardcode expectations for Locale.US.
+            DateFormat.is24Hour = null; // null == locale default (12 hour for US)
+            checkTimePattern(DateFormat.SHORT, "h:mm a");
+            checkTimePattern(DateFormat.MEDIUM, "h:mm:ss a");
+
+            DateFormat.is24Hour = true; // Explicit 24 hour.
+            checkTimePattern(DateFormat.SHORT, "HH:mm");
+            checkTimePattern(DateFormat.MEDIUM, "HH:mm:ss");
+
+            DateFormat.is24Hour = false; // Explicit 12 hour.
+            checkTimePattern(DateFormat.SHORT, "h:mm a");
+            checkTimePattern(DateFormat.MEDIUM, "h:mm:ss a");
+        } finally {
+            DateFormat.is24Hour = originalIs24Hour;
+        }
+    }
+
+    private static void checkTimePattern(int style, String expectedPattern) {
+        final Locale locale = Locale.US;
+        final Date current = new Date(1468250177000L); // 20160711 15:16:17 GMT
+        DateFormat format = DateFormat.getTimeInstance(style, locale);
+        String actualDateString = format.format(current);
+        SimpleDateFormat sdf = new SimpleDateFormat(expectedPattern, locale);
+        String expectedDateString = sdf.format(current);
+        assertEquals(expectedDateString, actualDateString);
+    }
+}