Test changeset not found page

test/system/changeset_test.rb

@@ -0,0 +1,19 @@
+require "application_system_test_case"
+
+class ChangesetSystemTest < ApplicationSystemTestCase
+  test "show existing changeset" do
+    changeset = create(:changeset)
+
+    visit changeset_path(changeset)
+    within_sidebar do
+      assert_text "Changeset: #{changeset.id}"
+    end
+  end
+
+  test "show error message for a changeset that doesn't exist" do
+    visit changeset_path(0)
+    within_sidebar do
+      assert_text "changeset #0 could not be found"
+    end
+  end
+end