ModelAttribute spec: Allow test to handle existing elements in `@@all`

When `ModelAttribute` instances are added to `@@all` directly in the
class, the test breaks. Make it a little more robust by checking change
in array size instead of total size.

Refs #4401

2 files changed, 6 insertions, 4 deletions

diff --git a/lib/model_attribute.rb b/lib/model_attribute.rb
index be5caea94..b1297d43d 100644
--- a/lib/model_attribute.rb
+++ b/lib/model_attribute.rb
@@ -14,4 +14,6 @@ class ModelAttribute
     @name = name
     @data_type = data_type
   end
+
+  define :journey_pattern, :name, :string
 end
diff --git a/spec/lib/model_attribute_spec.rb b/spec/lib/model_attribute_spec.rb
index 88d3997b6..da767cfed 100644
--- a/spec/lib/model_attribute_spec.rb
+++ b/spec/lib/model_attribute_spec.rb
@@ -1,11 +1,11 @@
 RSpec.describe ModelAttribute do
   describe ".define" do
     it "adds a new instance of ModelAttribute to @@all" do
-      ModelAttribute.define(:route, :name, :string)
+      expect do
+        ModelAttribute.define(:route, :name, :string)
+      end.to change { ModelAttribute.all.length }.by(1)
 
-      expect(ModelAttribute.all.length).to eq(1)
-
-      model_attr = ModelAttribute.all.first
+      model_attr = ModelAttribute.all.last
 
       expect(model_attr).to be_an_instance_of(ModelAttribute)
       expect(model_attr.klass).to eq(:route)