class_docstr: Test that an artifact defined in the first step
  is available in all steps downstream.
class_docstr_tok: ["Test","that","an","artifact","defined","in","the","first","step","is","available","in","all","steps","downstream","."]
code: def check_results(self, flow, checker):
      for step in flow:
          checker.assert_artifact(step.name, "data", "abc")
  
imports: from metaflow_test import MetaflowTest, ExpectationFailed, steps
label_desc: Use image node_id 4 for calling the BasicArtifactTest obj's underlying member method code with example usage: obj.check_results(flow, checker) without return types