From 1eb5b151236494b08a80813ee0ffc3bc2594f6bc Mon Sep 17 00:00:00 2001
From: Andrii Furmanets <furmanets.andriy@gmail.com>
Date: Fri, 16 Oct 2026 20:03:06 +0300
Subject: [PATCH] Inherit raise_on_mismatches from the superclass

Setting raise_on_mismatches on a base experiment class had no effect on
its subclasses, because the flag lives in a class instance variable.
Fall back to the superclass when a class hasn't set its own value.

Fixes #174
---
 README.md                         |  2 ++
 lib/scientist/experiment.rb       |  9 ++++++++-
 test/scientist/experiment_test.rb | 23 +++++++++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/README.md b/README.md
index e076498..59d8481 100644
--- a/README.md
+++ b/README.md
@@ -405,6 +405,8 @@ end
 MyExperiment.raise_on_mismatches = true
 ```
 
+Subclasses of `MyExperiment` inherit this setting unless they set their own.
+
 Scientist will raise a `Scientist::Experiment::MismatchError` exception if any observations don't match.
 
 #### Custom mismatch errors
diff --git a/lib/scientist/experiment.rb b/lib/scientist/experiment.rb
index 591b3a0..9f0d842 100644
--- a/lib/scientist/experiment.rb
+++ b/lib/scientist/experiment.rb
@@ -72,8 +72,15 @@ def raise_on_mismatches=(bool)
     end
 
     # Whether or not to raise a mismatch error when a mismatch occurs.
+    #
+    # Subclasses inherit the setting from their superclass unless they set
+    # their own.
     def raise_on_mismatches?
-      @raise_on_mismatches
+      if !@raise_on_mismatches.nil?
+        @raise_on_mismatches
+      elsif respond_to?(:superclass) && superclass.respond_to?(:raise_on_mismatches?)
+        superclass.raise_on_mismatches?
+      end
     end
   end
 
diff --git a/test/scientist/experiment_test.rb b/test/scientist/experiment_test.rb
index 434e673..aa00540 100644
--- a/test/scientist/experiment_test.rb
+++ b/test/scientist/experiment_test.rb
@@ -546,6 +546,29 @@ def @ex.raised(op, exception)
 
         assert_raises(Scientist::Experiment::MismatchError) { @ex.run }
       end
+
+      it "inherits the raise_on_mismatches class attribute from a superclass" do
+        subclass = Class.new(Fake)
+        Fake.raise_on_mismatches = true
+
+        ex = subclass.new
+        ex.use { "fine" }
+        ex.try { "not fine" }
+
+        assert_raises(Scientist::Experiment::MismatchError) { ex.run }
+      end
+
+      it "lets a subclass override the raise_on_mismatches class attribute" do
+        subclass = Class.new(Fake)
+        Fake.raise_on_mismatches = true
+        subclass.raise_on_mismatches = false
+
+        ex = subclass.new
+        ex.use { "fine" }
+        ex.try { "not fine" }
+
+        assert_equal "fine", ex.run
+      end
     end
 
     describe "MismatchError" do