Unit tests for predecessor

Author: jmwski

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

@@ -71,7 +71,7 @@ public static final String predecessor(String key) {
     Validation.validateNullableKey(key);
     Integer num = tryParseInt(key);
     if (num != null) {
-      if (Long.valueOf(num) - 1 < Integer.MIN_VALUE) {
+      if (num == Integer.MIN_VALUE) {
         return ChildKey.MIN_KEY_NAME;
       }
       return String.valueOf(num - 1);
@@ -98,7 +98,7 @@ public static final String successor(String key) {
     Validation.validateNullableKey(key);
     Integer num = tryParseInt(key);
     if (num != null) {
-      if (num + 1L > Integer.MAX_VALUE) {
+      if (num == Integer.MAX_VALUE) {
         // See https://firebase.google.com/docs/database/web/lists-of-data#data-order
         return String.valueOf(MIN_PUSH_CHAR);
       }

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

@@ -15,6 +15,7 @@
 package com.google.firebase.database;
 
 import static com.google.firebase.database.snapshot.ChildKey.MAX_KEY_NAME;
+import static com.google.firebase.database.snapshot.ChildKey.MIN_KEY_NAME;
 import static org.junit.Assert.assertEquals;
 
 import com.google.firebase.database.core.utilities.PushIdGenerator;
@@ -56,4 +57,21 @@ public void testSuccessorBasic() {
     assertEquals(
         PushIdGenerator.successor("abc" + MIN_PUSH_CHAR), "abc" + MIN_PUSH_CHAR + MIN_PUSH_CHAR);
   }
+
+  @Test
+  public void testPredecessorSpecialValue() {
+    assertEquals(
+        PushIdGenerator.predecessor(String.valueOf(MIN_PUSH_CHAR)),
+        String.valueOf(Integer.MAX_VALUE));
+    assertEquals(PushIdGenerator.predecessor(String.valueOf(Integer.MIN_VALUE)), MIN_KEY_NAME);
+  }
+
+  @Test
+  public void testPredecessorBasicValue() {
+    assertEquals(
+        PushIdGenerator.predecessor("abc"),
+        "abb"
+            + StringUtils.repeat(Character.toString(MAX_PUSH_CHAR), MAX_KEY_LEN - "abc".length()));
+    assertEquals(PushIdGenerator.predecessor("abc" + MIN_PUSH_CHAR), "abc");
+  }
 }