Extend tests

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

@@ -1,7 +1,30 @@
 - doc: |
     Test that default value doesn't need to be supplied
+  job: {}
+  outputs:
+    out:
+      class: File
+      asserts:
+      - that: has_text
+        text: "1"
+- doc: |
+    Test that null is replaced with default value
+  job:
+    required_int_with_default:
+      type: raw
+      value: null
+  outputs:
+    out:
+      class: File
+      asserts:
+      - that: has_text
+        text: "1"
+- doc: |
+    Test that empty string is not replaced and fails
   job:
-    input: {}
+    required_int_with_default:
+      type: raw
+      value: ""
   outputs:
     out:
       class: File