Added new loop test

tests/loop/opt-var-loop.cwl

@@ -0,0 +1,34 @@
+#!/usr/bin/env cwl-runner
+cwlVersion: v1.2
+class: Workflow
+$namespaces:
+  cwltool: "http://commonwl.org/cwltool#"
+requirements:
+  InlineJavascriptRequirement: {}
+
+inputs:
+  i1: int
+outputs:
+  o1:
+    type: int
+    outputSource: subworkflow/o1
+steps:
+  subworkflow:
+    run:
+      class: ExpressionTool
+      inputs:
+        i1: int
+        i2: int?
+      outputs:
+        o1: int
+      expression: >
+        ${return {'o1': inputs.i1 + 1};}
+    in:
+      i1: i1
+    out: [o1]
+    requirements:
+      cwltool:Loop:
+        loopWhen: $(inputs.i1 < 10)
+        loop:
+          i1: o1
+        outputMethod: last

tests/test_loop.py

@@ -235,6 +235,19 @@ def test_scatter_inside_loop() -> None:
     assert json.loads(stream.getvalue()) == expected
 
 
+def test_loop_opt_variable() -> None:
+    """Test a loop case with two variables but one is optional."""
+    stream = StringIO()
+    params = [
+        "--enable-ext",
+        get_data("tests/loop/opt-var-loop.cwl"),
+        get_data("tests/loop/single-var-loop-job.yml"),
+    ]
+    main(params, stdout=stream)
+    expected = {"o1": 10}
+    assert json.loads(stream.getvalue()) == expected
+
+
 def test_nested_loops() -> None:
     """Test a workflow with two nested loops."""
     stream = StringIO()