test: Add ParallelFor compile test over single artifact. (kubeflow#10531

)

* .

* formatting

sdk/python/kfp/compiler/compiler_test.py

@@ -838,6 +838,20 @@ def my_pipeline():
                 with dsl.ParallelFor(items=single_param_task.output) as item:
                     print_and_return(text=item)
 
+    def test_cannot_compile_parallel_for_with_single_artifact(self):
+
+        with self.assertRaisesRegex(
+                ValueError,
+                r'Cannot iterate over a single artifact using `dsl\.ParallelFor`\. Expected a list of artifacts as argument to `items`\.'
+        ):
+
+            @dsl.pipeline
+            def my_pipeline():
+                single_artifact_task = print_and_return_as_artifact(
+                    text='string')
+                with dsl.ParallelFor(items=single_artifact_task.output) as item:
+                    print_artifact(a=item)
+
     def test_pipeline_in_pipeline(self):
 
         @dsl.pipeline(name='graph-component')

sdk/python/kfp/dsl/for_loop.py

@@ -286,7 +286,7 @@ def from_pipeline_channel(
         object."""
         if not channel.is_artifact_list:
             raise ValueError(
-                'Cannot iterate over a single Artifact using `dsl.ParallelFor`. Expected a list of Artifacts as argument to `items`.'
+                'Cannot iterate over a single artifact using `dsl.ParallelFor`. Expected a list of artifacts as argument to `items`.'
             )
         return LoopArtifactArgument(
             items=channel,

sdk/python/kfp/dsl/for_loop_test.py

@@ -207,7 +207,7 @@ def test_loop_artifact_argument_from_single_pipeline_channel_raises_error(
             self, channel):
         with self.assertRaisesRegex(
                 ValueError,
-                r'Cannot iterate over a single Artifact using `dsl\.ParallelFor`\. Expected a list of Artifacts as argument to `items`\.'
+                r'Cannot iterate over a single artifact using `dsl\.ParallelFor`\. Expected a list of artifacts as argument to `items`\.'
         ):
             loop_argument = for_loop.LoopArtifactArgument.from_pipeline_channel(
                 channel)