Rewrite spec to test behaviour, not implementation

app/models/error_tracking/project_error_tracking_setting.rb

@@ -126,6 +126,10 @@ module ErrorTracking
       end
     end
 
+    def expire_issues_cache
+      Rails.cache.delete_matched(expand_cache_key('list_issues'))
+    end
+
     # http://HOST/api/0/projects/ORG/PROJECT
     # ->
     # http://HOST/ORG/PROJECT
@@ -140,15 +144,9 @@ module ErrorTracking
       Addressable::URI.join(api_url, '/').to_s
     end
 
-    def clear_cache(resource_prefix)
-      raise 'No resource prefix provided' unless resource_prefix
-
-      Rails.cache.delete_matched(cache_key(resource_prefix))
-    end
-
     private
 
-    def cache_key(resource_prefix)
+    def expand_cache_key(resource_prefix)
       klass_key = self.class.reactive_cache_key.call(self).join(':')
 
       "#{klass_key}:#{resource_prefix}*"

spec/models/error_tracking/project_error_tracking_setting_spec.rb

@@ -441,17 +441,17 @@ describe ErrorTracking::ProjectErrorTrackingSetting do
     end
   end
 
-  describe '#clear_cache' do
-    let(:key_prefix) { 'list_issues' }
-
+  describe '#expire_issues_cache', :use_clean_rails_memory_store_caching do
     it 'clears the cache' do
       klass_key = subject.class.reactive_cache_key.call(subject).join(':')
+      key = "#{klass_key}:list_issues:some_suffix"
+      Rails.cache.write(key, 1)
+
+      expect(Rails.cache.exist?(key)).to eq(true)
 
-      expect(Rails.cache)
-        .to receive(:delete_matched)
-        .with("#{klass_key}:#{key_prefix}*")
+      subject.expire_issues_cache
 
-      subject.clear_cache(key_prefix)
+      expect(Rails.cache.exist?(key)).to eq(false)
     end
   end
 end