[Tests] add test for pipeline import. (#4276)

* add test for pipeline import.

* Update tests/others/test_dependencies.py
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

* address suggestions

---------
Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

tests/others/test_dependencies.py

@@ -14,6 +14,7 @@
 
 import inspect
 import unittest
+from importlib import import_module
 
 
 class DependencyTester(unittest.TestCase):
@@ -37,3 +38,13 @@ class DependencyTester(unittest.TestCase):
                     elif backend == "invisible_watermark":
                         backend = "invisible-watermark"
                     assert backend in deps, f"{backend} is not in the deps table!"
+
+    def test_pipeline_imports(self):
+        import diffusers
+        import diffusers.pipelines
+
+        all_classes = inspect.getmembers(diffusers, inspect.isclass)
+        for cls_name, cls_module in all_classes:
+            if hasattr(diffusers.pipelines, cls_name):
+                pipeline_folder_module = ".".join(str(cls_module.__module__).split(".")[:3])
+                _ = import_module(pipeline_folder_module, str(cls_name))