Add unit tests for successor

Author: jmwski

firebase-database/src/androidTest/java/com/google/firebase/database/QueryTest.java

@@ -771,7 +771,7 @@ public void onCancelled(DatabaseError error) {}
   }
 
   @Test
-  public void setLimitEnsureChildRemovedAndChildAddedHitWhenLimitIsHitFromFrontWithStartAfter()
+  public void setLimitEnsureChildRemovedAndChildAddedHitWhenDataEntersLimitWithStartAfter()
       throws DatabaseException, TestFailure, ExecutionException, TimeoutException,
           InterruptedException {
     DatabaseReference ref = IntegrationTestHelpers.getRandomNode();

firebase-database/src/main/java/com/google/firebase/database/core/utilities/PushIdGenerator.java

@@ -69,7 +69,7 @@ public static final String successor(String key) {
     Validation.validateNullableKey(key);
     Integer num = tryParseInt(key);
     if (num != null) {
-      if (Long.valueOf(num) + 1L > Integer.MAX_VALUE) {
+      if (num + 1L > Integer.MAX_VALUE) {
         // See https://firebase.google.com/docs/database/web/lists-of-data#data-order
         return String.valueOf(MIN_PUSH_CHAR);
       }
@@ -86,7 +86,6 @@ public static final String successor(String key) {
     }
 
     int i = next.length() - 1;
-
     while (i >= 0 && next.charAt(i) == MAX_PUSH_CHAR) {
       i--;
     }

firebase-database/src/test/java/com/google/firebase/database/PushIdGeneratorTest.java

@@ -0,0 +1,59 @@
+// Copyright 2021 Google LLC
+//
+// 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 com.google.firebase.database;
+
+import static com.google.firebase.database.snapshot.ChildKey.MAX_KEY_NAME;
+import static org.junit.Assert.assertEquals;
+
+import com.google.firebase.database.core.utilities.PushIdGenerator;
+import org.codehaus.plexus.util.StringUtils;
+import org.junit.Test;
+import org.robolectric.RobolectricTestRunner;
+import org.robolectric.annotation.Config;
+
+@org.junit.runner.RunWith(RobolectricTestRunner.class)
+@Config(manifest = Config.NONE)
+public class PushIdGeneratorTest {
+
+  private static final char MIN_PUSH_CHAR = '-';
+
+  private static final char MAX_PUSH_CHAR = 'z';
+
+  private static final int MAX_KEY_LEN = 786;
+
+  @Test
+  public void testSuccessorSpecialValue() {
+    assertEquals(
+        PushIdGenerator.successor(String.valueOf(Integer.MAX_VALUE)),
+        Character.toString(MIN_PUSH_CHAR));
+    assertEquals(
+        PushIdGenerator.successor(
+            StringUtils.repeat(Character.toString(MAX_PUSH_CHAR), MAX_KEY_LEN)),
+        MAX_KEY_NAME);
+  }
+
+  @Test
+  public void testSuccessorBasic() {
+    assertEquals(PushIdGenerator.successor("abc"), "abc" + MIN_PUSH_CHAR);
+    assertEquals(
+        PushIdGenerator.successor(
+            "abc"
+                + StringUtils.repeat(
+                    Character.toString(MAX_PUSH_CHAR), MAX_KEY_LEN - "abc".length())),
+        "abd");
+    assertEquals(
+        PushIdGenerator.successor("abc" + MIN_PUSH_CHAR), "abc" + MIN_PUSH_CHAR + MIN_PUSH_CHAR);
+  }
+}