Test filter null tool in workflow

lib/galaxy_test/workflow/filter_null.gxwf-tests.yml

@@ -0,0 +1,32 @@
+- doc: |
+    Test to verify filter null tool keeps non-null datasets.
+  job:
+    input_collection:
+      collection_type: list
+      elements:
+        - identifier: first
+          content: "abc"
+    when:
+      value: true
+      type: raw
+  outputs:
+    out:
+      class: Collection
+      collection_type: list
+      element_count: 1
+- doc: |
+    Test to verify filter null tool discards null datasets.
+  job:
+    input_collection:
+      collection_type: list
+      elements:
+        - identifier: first
+          content: "abc"
+    when:
+      value: false
+      type: raw
+  outputs:
+    out:
+      class: Collection
+      collection_type: list
+      element_count: 0

lib/galaxy_test/workflow/filter_null.gxwf.yml

@@ -0,0 +1,22 @@
+class: GalaxyWorkflow
+inputs:
+  input_collection:
+    type: data_collection
+  when:
+    type: boolean
+outputs:
+  out:
+    outputSource: filter_null/output
+steps:
+  cat:
+    tool_id: cat
+    in:
+      input1:
+        source: input_collection
+      when:
+        source: when
+    when: $(inputs.when)
+  filter_null:
+    tool_id: '__FILTER_NULL__'
+    in:
+      input: cat/out_file1