Pin the default time zone and locale to make ICU formatting tests mor…

…e resilient

executors/icu4j/73/executor-icu4j/src/test/java/org/unicode/conformance/messageformat2/MessageFormatterTest.java

@@ -2,10 +2,17 @@
 
 import static org.junit.Assert.assertEquals;
 
+import com.ibm.icu.util.ULocale;
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
+import java.util.Locale;
+import java.util.TimeZone;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.TestName;
 import org.unicode.conformance.testtype.messageformat2.MFInputArg;
 import org.unicode.conformance.testtype.messageformat2.MFInputArgType;
 import org.unicode.conformance.testtype.messageformat2.MFTestSubType;
@@ -14,6 +21,78 @@
 
 public class MessageFormatterTest {
 
+  /**
+   * The default locale used for all of our tests. Used in @Before
+   */
+  protected final static Locale defaultLocale = Locale.US;
+
+  /**
+   * The default time zone for all of our tests. Used in @Before
+   */
+  protected final static TimeZone defaultTimeZone = TimeZone.getTimeZone("America/Los_Angeles");
+
+  private com.ibm.icu.util.TimeZone testStartDefaultIcuTz;
+
+  private java.util.TimeZone testStartDefaultJdkTz;
+
+  private com.ibm.icu.util.ULocale testStartDefaultULocale;
+
+  private java.util.Locale testStartDefaultLocale;
+
+  @Rule
+  public TestName name = new TestName();
+
+  // Copying test setup behavior from ICU4J CoreTestFmwk / TestFmwk, which
+  // ensures we pin the default locale and TZ during the test. ICU Formatters
+  // implicitly use the system's default locale and TZ.
+  @Before
+  public final void setup() {
+    // Just like TestFmwk initializes JDK TimeZone and Locale before every test,
+    // do the same for ICU TimeZone and ULocale.
+    ULocale.setDefault(ULocale.forLocale(defaultLocale));
+    com.ibm.icu.util.TimeZone.setDefault(
+        com.ibm.icu.util.TimeZone.getTimeZone(defaultTimeZone.getID()));
+
+    // Save starting timezones
+    testStartDefaultIcuTz = com.ibm.icu.util.TimeZone.getDefault();
+    testStartDefaultJdkTz = java.util.TimeZone.getDefault();
+
+    // Save starting locales
+    testStartDefaultULocale = com.ibm.icu.util.ULocale.getDefault();
+    testStartDefaultLocale = java.util.Locale.getDefault();
+  }
+
+  // Copying test teardown beahvior from ICU4J CoreTestFmwk, corresponding to
+  // the setup work.
+  @After
+  public final void teardown() {
+    String testMethodName = name.getMethodName();
+
+    // Assert that timezones are in a good state
+
+    com.ibm.icu.util.TimeZone testEndDefaultIcuTz = com.ibm.icu.util.TimeZone.getDefault();
+    java.util.TimeZone testEndDefaultJdkTz = java.util.TimeZone.getDefault();
+
+    assertEquals("In [" + testMethodName + "] Test should keep in sync ICU & JDK TZs",
+        testEndDefaultIcuTz.getID(),
+        testEndDefaultJdkTz.getID());
+
+    assertEquals("In [" + testMethodName + "] Test should reset ICU default TZ",
+        testStartDefaultIcuTz.getID(), testEndDefaultIcuTz.getID());
+    assertEquals("In [" + testMethodName + "] Test should reset JDK default TZ",
+        testStartDefaultJdkTz.getID(), testEndDefaultJdkTz.getID());
+
+    // Assert that locales are in a good state
+
+    com.ibm.icu.util.ULocale testEndDefaultULocale = com.ibm.icu.util.ULocale.getDefault();
+    java.util.Locale testEndDefaultLocale = java.util.Locale.getDefault();
+
+    assertEquals("In [" + testMethodName + "] Test should reset ICU ULocale",
+        testStartDefaultULocale.toLanguageTag(), testEndDefaultULocale.toLanguageTag());
+    assertEquals("In [" + testMethodName + "] Test should reset JDK Locale",
+        testStartDefaultLocale.toLanguageTag(), testEndDefaultLocale.toLanguageTag());
+  }
+
   @Test
   public void testGetFormattedMessage() {
     // Setup