FIX: compile triplet loss within keras model (tensorflow#298)

* FIX: compile triplet loss within keras model

* remove dummy assertion

* add a testcase when the shape of y_true is invalid

* remove testcase of invalid shape

tensorflow_addons/losses/triplet.py

@@ -73,9 +73,8 @@ def triplet_semihard_loss(y_true, y_pred, margin=1.0):
       margin: Float, margin term in the loss definition.
     """
     labels, embeddings = y_true, y_pred
-    # Reshape [batch_size] label tensor to a [batch_size, 1] label tensor.
+    # Reshape label tensor to [batch_size, 1].
     lshape = tf.shape(labels)
-    assert lshape.shape == 1
     labels = tf.reshape(labels, [lshape[0], 1])
 
     # Build pairwise squared distance matrix.

tensorflow_addons/losses/triplet_test.py

@@ -104,6 +104,13 @@ def test_unweighted(self):
         loss = cce_obj(y_true, y_pred)
         self.assertAlmostEqual(self.evaluate(loss), loss_np, 3)
 
+    def test_keras_model_compile(self):
+        model = tf.keras.models.Sequential([
+            tf.keras.layers.Input(shape=(784,)),
+            tf.keras.layers.Dense(10),
+        ])
+        model.compile(loss="triplet_semihard_loss", optimizer="adam")
+
 
 if __name__ == '__main__':
     tf.test.main()