BUGFIX: Pass values, not observations, to the .diff block

Author: geeksam

app/models/lab_tech/result.rb

@@ -59,7 +59,14 @@ def record_a_science(scientist_result, diff_with: nil)
 
       record_observation scientist_result.control
       scientist_result.candidates.each do |candidate|
-        diff = diff_with&.call(scientist_result.control, candidate)
+        diff = nil
+        if diff_with
+          # Pass values to the diff block, not the observations themselves
+          cont = scientist_result.control.value
+          cand = candidate.value
+          diff = diff_with&.call(cont, cand)
+        end
+
         record_observation candidate, diff: diff
       end
 

spec/models/lab_tech/experiment_spec.rb

@@ -100,7 +100,12 @@ def wtf
             e.use { :control }
             e.try { :candidate }
 
-            e.diff { |control, candidate| "this is a diff" }
+            e.diff { |control, candidate|
+              # Make sure we pass values to the diff block, not the observations themselves
+              raise "nope" if control.is_a?(Scientist::Observation)
+              raise "nope" if candidate.is_a?(Scientist::Observation)
+              "this is a diff"
+            }
           end
 
           result = experiment.results.first