Add a validate_regex method and specs.

app/models/miq_request_workflow/dialog_field_validation.rb

@@ -37,4 +37,12 @@ def validate_regex(_field, _values, dlg, fld, value)
       error
     end
   end
+
+  def validate_blacklist(_field, _values, dlg, fld, value)
+    blacklist = fld[:blacklist]
+    return _("%{name} is required") % {:name => required_description(dlg, fld)} if value.blank?
+    if blacklist && blacklist.include?(value)
+      _("%{name} may not contain blacklisted value") % {:name => required_description(dlg, fld)}
+    end
+  end
 end

spec/models/miq_request_workflow_spec.rb

@@ -358,6 +358,22 @@
     end
   end
 
+  context "#validate_blacklist" do
+    let(:blacklist) { {:blacklist => ['foo', 'bar']} }
+
+    it "returns nil if the value is not blacklisted" do
+      expect(workflow.validate_blacklist(nil, {}, {}, blacklist, 'test')).to be_nil
+    end
+
+    it "returns a formatted message when the value is blacklisted" do
+      expect(workflow.validate_blacklist(nil, {}, {}, blacklist, 'foo')).to eq("'/' may not contain blacklisted value")
+    end
+
+    it "returns an error when no value exists" do
+      expect(workflow.validate_blacklist(nil, {}, {}, blacklist, '')).to eq "'/' is required"
+    end
+  end
+
   context "#validate regex" do
     let(:regex) { {:required_regex => "^[email protected]$"} }
     let(:regex_two) { {:required_regex => "^n$"} }