Merge pull request #46863 from ghiculescu/assert-diffrence-message

Include amount changed by in `assert_difference` failure message
rails · Jan 7, 2023 · 05acc18 · 05acc18
2 parents 15a0325 + 293349c
commit 05acc18
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Showing 3 changed files with 38 additions and 5 deletions.
diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
@@ -1,3 +1,25 @@
+*   `assert_difference` message now includes what changed.
+
+    This makes it easier to debug non-obvious failures.
+
+    Before:
+
+    ```
+    "User.count" didn't change by 32.
+    Expected: 1611
+      Actual: 1579
+    ```
+
+    After:
+
+    ```
+    "User.count" didn't change by 32, but by 0.
+    Expected: 1611
+      Actual: 1579
+    ```
+
+    *Alex Ghiculescu*
+
 *   Add ability to match exception messages to `assert_raises` assertion
 
     Instead of this

diff --git a/activesupport/lib/active_support/testing/assertions.rb b/activesupport/lib/active_support/testing/assertions.rb
@@ -116,9 +116,10 @@ def assert_difference(expression, *args, &block)
         retval = _assert_nothing_raised_or_warn("assert_difference", &block)
 
         expressions.zip(exps, before) do |(code, diff), exp, before_value|
-          error  = "#{code.inspect} didn't change by #{diff}"
+          actual = exp.call
+          error  = "#{code.inspect} didn't change by #{diff}, but by #{actual - before_value}"
           error  = "#{message}.\n#{error}" if message
-          assert_equal(before_value + diff, exp.call, error)
+          assert_equal(before_value + diff, actual, error)
         end
 
         retval

diff --git a/activesupport/test/test_case_test.rb b/activesupport/test/test_case_test.rb
@@ -54,7 +54,7 @@ def test_assert_no_difference_fail
         @object.increment
       end
     end
-    assert_equal "\"@object.num\" didn't change by 0.\nExpected: 0\n  Actual: 1", error.message
+    assert_equal "\"@object.num\" didn't change by 0, but by 1.\nExpected: 0\n  Actual: 1", error.message
   end
 
   def test_assert_no_difference_with_message_fail
@@ -63,7 +63,7 @@ def test_assert_no_difference_with_message_fail
         @object.increment
       end
     end
-    assert_equal "Object Changed.\n\"@object.num\" didn't change by 0.\nExpected: 0\n  Actual: 1", error.message
+    assert_equal "Object Changed.\n\"@object.num\" didn't change by 0, but by 1.\nExpected: 0\n  Actual: 1", error.message
   end
 
   def test_assert_no_difference_with_multiple_expressions_pass
@@ -157,7 +157,17 @@ def test_hash_of_expressions_with_message
         @object.increment
       end
     end
-    assert_equal "Object Changed.\n\"@object.num\" didn't change by 0.\nExpected: 0\n  Actual: 1", error.message
+    assert_equal "Object Changed.\n\"@object.num\" didn't change by 0, but by 1.\nExpected: 0\n  Actual: 1", error.message
+  end
+
+  def test_assert_difference_message_includes_change
+    error = assert_raises Minitest::Assertion do
+      assert_difference "@object.num", +5 do
+        @object.increment
+        @object.increment
+      end
+    end
+    assert_equal "\"@object.num\" didn't change by 5, but by 2.\nExpected: 5\n  Actual: 2", error.message
   end
 
   def test_hash_of_lambda_expressions