Add tests to demonstrate the issue

Run the FieldNamingTest with the JVM options: `-Duser.language=tr
-Duser.region=TR`

gson/src/test/java/com/google/gson/functional/FieldNamingTest.java

@@ -21,6 +21,8 @@ import static com.google.gson.FieldNamingPolicy.LOWER_CASE_WITH_DASHES;
 import static com.google.gson.FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES;
 import static com.google.gson.FieldNamingPolicy.UPPER_CAMEL_CASE;
 import static com.google.gson.FieldNamingPolicy.UPPER_CAMEL_CASE_WITH_SPACES;
+
+import com.google.gson.FieldNamingPolicy;
 import com.google.gson.Gson;
 import com.google.gson.GsonBuilder;
 import com.google.gson.annotations.SerializedName;
@@ -28,45 +30,51 @@ import junit.framework.TestCase;
 
 public final class FieldNamingTest extends TestCase {
   public void testIdentity() {
-    Gson gson = new GsonBuilder().setFieldNamingPolicy(IDENTITY).create();
+    Gson gson = getGsonWithNamingPolicy(IDENTITY);
     assertEquals("{'lowerCamel':1,'UpperCamel':2,'_lowerCamelLeadingUnderscore':3," +
         "'_UpperCamelLeadingUnderscore':4,'lower_words':5,'UPPER_WORDS':6," +
-        "'annotatedName':7}",
+        "'annotatedName':7,'lowerId':8}",
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
   public void testUpperCamelCase() {
-    Gson gson = new GsonBuilder().setFieldNamingPolicy(UPPER_CAMEL_CASE).create();
+    Gson gson = getGsonWithNamingPolicy(UPPER_CAMEL_CASE);
     assertEquals("{'LowerCamel':1,'UpperCamel':2,'_LowerCamelLeadingUnderscore':3," +
         "'_UpperCamelLeadingUnderscore':4,'Lower_words':5,'UPPER_WORDS':6," +
-        "'annotatedName':7}",
+        "'annotatedName':7,'LowerId':8}",
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
   public void testUpperCamelCaseWithSpaces() {
-    Gson gson = new GsonBuilder().setFieldNamingPolicy(UPPER_CAMEL_CASE_WITH_SPACES).create();
+    Gson gson = getGsonWithNamingPolicy(UPPER_CAMEL_CASE_WITH_SPACES);
     assertEquals("{'Lower Camel':1,'Upper Camel':2,'_Lower Camel Leading Underscore':3," +
         "'_ Upper Camel Leading Underscore':4,'Lower_words':5,'U P P E R_ W O R D S':6," +
-        "'annotatedName':7}",
+        "'annotatedName':7,'Lower Id':8}",
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
   public void testLowerCaseWithUnderscores() {
-    Gson gson = new GsonBuilder().setFieldNamingPolicy(LOWER_CASE_WITH_UNDERSCORES).create();
+    Gson gson = getGsonWithNamingPolicy(LOWER_CASE_WITH_UNDERSCORES);
     assertEquals("{'lower_camel':1,'upper_camel':2,'_lower_camel_leading_underscore':3," +
         "'__upper_camel_leading_underscore':4,'lower_words':5,'u_p_p_e_r__w_o_r_d_s':6," +
-        "'annotatedName':7}",
+        "'annotatedName':7,'lower_id':8}",
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
   public void testLowerCaseWithDashes() {
-    Gson gson = new GsonBuilder().setFieldNamingPolicy(LOWER_CASE_WITH_DASHES).create();
+    Gson gson = getGsonWithNamingPolicy(LOWER_CASE_WITH_DASHES);
     assertEquals("{'lower-camel':1,'upper-camel':2,'_lower-camel-leading-underscore':3," +
         "'_-upper-camel-leading-underscore':4,'lower_words':5,'u-p-p-e-r_-w-o-r-d-s':6," +
-        "'annotatedName':7}",
+        "'annotatedName':7,'lower-id':8}",
         gson.toJson(new TestNames()).replace('\"', '\''));
   }
 
+  private Gson getGsonWithNamingPolicy(FieldNamingPolicy fieldNamingPolicy){
+    return new GsonBuilder()
+      .setFieldNamingPolicy(fieldNamingPolicy)
+        .create();
+  }
+
   @SuppressWarnings("unused") // fields are used reflectively
   private static class TestNames {
     int lowerCamel = 1;
@@ -76,5 +84,6 @@ public final class FieldNamingTest extends TestCase {
     int lower_words = 5;
     int UPPER_WORDS = 6;
     @SerializedName("annotatedName") int annotated = 7;
+    int lowerId = 8;
   }
 }