Improve Sequential test coverage

keras_core/models/sequential.py

@@ -40,7 +40,7 @@ class Sequential(Model):
         ):
             raise ValueError(
                 f"Sequential model '{self.name}' has already been configured to "
-                f"use input shape {self._layers[0].batch_input_shape}. You cannot add "
+                f"use input shape {self._layers[0].batch_shape}. You cannot add "
                 f"a different Input layer to it."
             )
 

keras_core/models/sequential_test.py

@@ -94,5 +94,35 @@ class SequentialTest(testing.TestCase):
     def test_dict_inputs(self):
         pass
 
+    def test_errors(self):
+        # Trying to pass 2 Inputs
+        model = Sequential()
+        model.add(Input(shape=(2,), batch_size=3))
+        with self.assertRaisesRegex(ValueError, "already been configured"):
+            model.add(Input(shape=(2,), batch_size=3))
+        with self.assertRaisesRegex(ValueError, "already been configured"):
+            model.add(layers.InputLayer(shape=(2,), batch_size=3))
+
+        # Same name 2x
+        model = Sequential()
+        model.add(layers.Dense(2, name="dense"))
+        with self.assertRaisesRegex(ValueError, "should have unique names"):
+            model.add(layers.Dense(2, name="dense"))
+
+        # No layers
+        model = Sequential()
+        x = np.random.random((3, 2))
+        with self.assertRaisesRegex(ValueError, "no layers"):
+            model(x)
+
+        # Build conflict
+        model = Sequential()
+        model.add(Input(shape=(2,), batch_size=3))
+        model.add(layers.Dense(2))
+        with self.assertRaisesRegex(ValueError, "already been configured"):
+            model.build((3, 4))
+        # But this works
+        model.build((3, 2))
+
     def test_serialization(self):
         pass