added single gpu train test

tests/test_models.py

@@ -27,6 +27,34 @@ np.random.seed(SEED)
 # TESTS
 # ------------------------------------------------------------------------
 
+def test_amp_single_gpu():
+    """
+    Make sure DDP + AMP work
+    :return:
+    """
+    if not torch.cuda.is_available():
+        warnings.warn('test_amp_gpu_ddp cannot run.'
+                      'Rerun on a GPU node to run this test')
+        return
+    if not torch.cuda.device_count() > 1:
+        warnings.warn('test_amp_gpu_ddp cannot run.'
+                      'Rerun on a node with 2+ GPUs to run this test')
+        return
+
+    hparams = get_hparams()
+    model = LightningTestModel(hparams)
+
+    trainer_options = dict(
+        progress_bar=True,
+        max_nb_epochs=1,
+        gpus=[0],
+        distributed_backend='dp',
+        use_amp=True
+    )
+
+    run_gpu_model_test(trainer_options, model, hparams)
+
+
 def test_cpu_restore_training():
     """
     Verify continue training session on CPU