Add boundary tests for JsonTreeWriter.endArray() error handling (#2988)

* Add boundary tests for JsonTreeWriter.endArray() error handling

* Update JsonTreeWriterTest.java

Author: lmj798

gson/src/test/java/com/google/gson/internal/bind/JsonTreeWriterTest.java

@@ -281,4 +281,25 @@ public void testOverrides() {
             "getSerializeNulls()");
     MoreAsserts.assertOverridesMethods(JsonWriter.class, JsonTreeWriter.class, ignoredMethods);
   }
+
+  @Test
+  public void testEndArrayOnEmptyStackThrows() {
+    JsonTreeWriter writer = new JsonTreeWriter();
+    assertThrows(IllegalStateException.class, () -> writer.endArray());
+  }
+
+  @Test
+  public void testEndArrayWithPendingNameThrows() throws IOException {
+    JsonTreeWriter writer = new JsonTreeWriter();
+    writer.beginObject();
+    writer.name("test");
+    assertThrows(IllegalStateException.class, () -> writer.endArray());
+  }
+
+  @Test
+  public void testEndArrayWhenStackTopIsNotArrayThrows() throws IOException {
+    JsonTreeWriter writer = new JsonTreeWriter();
+    writer.beginObject();
+    assertThrows(IllegalStateException.class, () -> writer.endArray());
+  }
 }