Add a utility method for getting alternate forms of (Benin) phone numbers

service/src/test/java/org/whispersystems/textsecuregcm/util/UtilTest.java

@@ -0,0 +1,42 @@
+/*
+ * Copyright 2024 Signal Messenger, LLC
+ * SPDX-License-Identifier: AGPL-3.0-only
+ */
+
+package org.whispersystems.textsecuregcm.util;
+
+import com.google.i18n.phonenumbers.PhoneNumberUtil;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class UtilTest {
+
+  @ParameterizedTest
+  @MethodSource
+  void getAlternateForms(final String phoneNumber, final List<String> expectedAlternateForms) {
+    assertEquals(expectedAlternateForms, Util.getAlternateForms(phoneNumber));
+  }
+
+  static List<Arguments> getAlternateForms() {
+    final String usE164 = PhoneNumberUtil.getInstance().format(
+        PhoneNumberUtil.getInstance().getExampleNumber("US"), PhoneNumberUtil.PhoneNumberFormat.E164);
+
+    // libphonenumber 8.13.50 and on generate new-format numbers for Benin
+    final String newFormatBeninE164 = PhoneNumberUtil.getInstance()
+        .format(PhoneNumberUtil.getInstance().getExampleNumber("BJ"), PhoneNumberUtil.PhoneNumberFormat.E164);
+
+    final String oldFormatBeninE164 = newFormatBeninE164.replaceFirst("01", "");
+
+    return List.of(
+        Arguments.of(usE164, List.of(usE164)),
+        Arguments.of(newFormatBeninE164, List.of(newFormatBeninE164, oldFormatBeninE164)),
+        Arguments.of(oldFormatBeninE164, List.of(oldFormatBeninE164, newFormatBeninE164))
+    );
+  }
+}