test: ensure RspecApiDocumentation.configuration.app is set

Author: bf4

spec/rack_test_client_spec.rb

@@ -9,6 +9,10 @@
 
   subject { test_client }
 
+  before do
+    RspecApiDocumentation.configuration.app ||= context.app
+  end
+
   it { expect(subject).to be_a(RspecApiDocumentation::RackTestClient) }
 
   its(:context) { should equal(context) }