feat : variants implementation

Author: reeshika-h

src/test/java/com/contentstack/sdk/TestEntry.java

@@ -66,6 +66,50 @@ public void onCompletion(ResponseType responseType, Error error) {
         });
         logger.info("passed..");
     }
+    @Test
+    void VariantsTestSingleUid(){
+        entry = stack.contentType(CONTENT_TYPE).entry(entryUid).variants("  cs672c33271558d8b0 ");
+        entry.fetch(new EntryResultCallBack() {
+            @Override
+            public void onCompletion(ResponseType responseType, Error error) {
+                assertEquals("cs672c33271558d8b0", entry.getHeaders().get("x-cs-variant-uid"));
+               System.out.println(entry.toJSON());
+            }
+        });
+    }
+    @Test
+    void VariantsTestArray(){
+        entry = stack.contentType(CONTENT_TYPE).entry(entryUid).variants(new String[]{" cs672c33271558d8b0"," cs321fbc07ec71861b"," cs321fbc07ec71861b "});
+        entry.fetch(new EntryResultCallBack() {
+            @Override
+            public void onCompletion(ResponseType responseType, Error error) {
+               System.out.println(entry.toJSON());
+            }
+        });
+    }
+    
+    @Test
+    void VariantsTestArrayWithMixedElements() {
+        entry = stack.contentType(CONTENT_TYPE).entry(entryUid).variants(new String[]{"", " cs672c33271558d8b0 ", null, "   "});
+        entry.fetch(new EntryResultCallBack() {
+            @Override
+            public void onCompletion(ResponseType responseType, Error error) {
+                System.out.println(entry.toJSON());
+            }
+        });
+    }
+
+    @Test
+    void VariantsTestNullString() {
+    entry = stack.contentType(CONTENT_TYPE).entry(entryUid).variants((String) null);
+    entry.fetch(new EntryResultCallBack() {
+        @Override
+        public void onCompletion(ResponseType responseType, Error error) {
+            assertNull(entry.getHeaders().get("x-cs-variant-uid"));
+            System.out.println(entry.toJSON());
+        }
+    });
+    }
 
     @Test
     void VariantsTestSingleUid() {