Helper function to return the unique name for subscription info

Many classes within Settings have access to the subscription info, rather
than only having access to the subscription id. For these classes, it is
more convenient to have a helper method where the whole subscription
info can be passed in, rather than having to call the
getSubscriptionId() helper method in so many locations within the
telephony settings codebase.

Bug: 150370656
Bug: 148303118
Test: atest -c SubscriptionUtilTest
Change-Id: I181960933ab8610d5572b7a7d6671fab8c1dbd22

tests/unit/src/com/android/settings/network/SubscriptionUtilTest.java

@@ -360,6 +360,26 @@ public class SubscriptionUtilTest {
         assertTrue(TextUtils.isEmpty(name));
     }
 
+    @Test
+    public void getUniqueDisplayName_fullSubscriptionInfo_correctNameReturned() {
+        // Each subscription's default display name is unique.
+        final SubscriptionInfo info1 = mock(SubscriptionInfo.class);
+        when(info1.getSubscriptionId()).thenReturn(SUBID_1);
+        when(info1.getDisplayName()).thenReturn(CARRIER_1);
+        when(mSubMgr.getActiveSubscriptionInfoList()).thenReturn(
+                Arrays.asList(info1));
+
+        TelephonyManager sub1Telmgr = mock(TelephonyManager.class);
+        when(sub1Telmgr.getLine1Number()).thenReturn("1112223333");
+        when(mTelMgr.createForSubscriptionId(SUBID_1)).thenReturn(sub1Telmgr);
+
+        final CharSequence name =
+                SubscriptionUtil.getUniqueSubscriptionDisplayName(info1, mContext);
+
+        assertThat(name).isNotNull();
+        assertEquals(CARRIER_1, name);
+    }
+
     @Test
     public void isInactiveInsertedPSim_nullSubInfo_doesNotCrash() {
         assertThat(SubscriptionUtil.isInactiveInsertedPSim(null)).isFalse();