Update assert_changes and assert_no_changes to use assert_equal

This provides better more specific diffs when comparing complex objects.

Reverts bbe437faec.

Closes #37507. Closes #38220.

Co-authored-by: michdsouza <michd2005@gmail.com>
Co-authored-by: Rahul Purohit <rahulpuroht@gmail.com>
Co-authored-by: Nicholas Koh <nkohwl@gmail.com>

activesupport/lib/active_support/testing/assertions.rb

@@ -177,7 +177,7 @@ module ActiveSupport
         retval = assert_nothing_raised(&block)
 
         unless from == UNTRACKED
-          error = "#{expression.inspect} isn't #{from.inspect}"
+          error = "Expected change from #{from.inspect}"
           error = "#{message}.\n#{error}" if message
           assert from === before, error
         end
@@ -187,12 +187,10 @@ module ActiveSupport
         error = "#{expression.inspect} didn't change"
         error = "#{error}. It was already #{to}" if before == to
         error = "#{message}.\n#{error}" if message
-        assert before != after, error
+        assert_not_equal before, after, error
 
         unless to == UNTRACKED
-          error = "#{expression.inspect} didn't change to as expected\n"
-          error = "#{error}Expected: #{to.inspect}\n"
-          error = "#{error}  Actual: #{after.inspect}"
+          error = "Expected change to #{to}\n"
           error = "#{message}.\n#{error}" if message
           assert to === after, error
         end
@@ -219,9 +217,14 @@ module ActiveSupport
         retval = assert_nothing_raised(&block)
         after = exp.call
 
-        error = "#{expression.inspect} did change to #{after}"
+        error = "#{expression.inspect} changed"
         error = "#{message}.\n#{error}" if message
-        assert before == after, error
+
+        if before.nil?
+          assert_nil after, error
+        else
+          assert_equal before, after, error
+        end
 
         retval
       end

activesupport/test/test_case_test.rb

@@ -192,7 +192,7 @@ class AssertionsTest < ActiveSupport::TestCase
         @object.increment
       end
     end
-    assert_equal "\"@object.num\" isn't nil", error.message
+    assert_equal "Expected change from nil", error.message
   end
 
   def test_assert_changes_with_to_option
@@ -208,7 +208,7 @@ class AssertionsTest < ActiveSupport::TestCase
       end
     end
 
-    assert_equal "\"@object.num\" didn't change. It was already 0", error.message
+    assert_equal "\"@object.num\" didn't change. It was already 0.\nExpected 0 to not be equal to 0.", error.message
   end
 
   def test_assert_changes_with_wrong_to_option
@@ -272,12 +272,12 @@ class AssertionsTest < ActiveSupport::TestCase
 
   def test_assert_changes_with_message
     error = assert_raises Minitest::Assertion do
-      assert_changes "@object.num", "@object.num should 1", to: 1 do
+      assert_changes "@object.num", "@object.num should be 1", to: 1 do
         @object.decrement
       end
     end
 
-    assert_equal "@object.num should 1.\n\"@object.num\" didn't change to as expected\nExpected: 1\n  Actual: -1", error.message
+    assert_equal "@object.num should be 1.\nExpected change to 1\n", error.message
   end
 
   def test_assert_no_changes_pass
@@ -293,7 +293,29 @@ class AssertionsTest < ActiveSupport::TestCase
       end
     end
 
-    assert_equal "@object.num should not change.\n\"@object.num\" did change to 1", error.message
+    assert_equal "@object.num should not change.\n\"@object.num\" changed.\nExpected: 0\n  Actual: 1", error.message
+  end
+
+  def test_assert_no_changes_with_long_string_wont_output_everything
+    lines = "HEY\n" * 12
+
+    error = assert_raises Minitest::Assertion do
+      assert_no_changes "lines" do
+        lines += "HEY ALSO\n"
+      end
+    end
+
+    assert_match <<~output, error.message
+      "lines" changed.
+      --- expected
+      +++ actual
+      @@ -10,4 +10,5 @@
+       HEY
+       HEY
+       HEY
+      +HEY ALSO
+       "
+    output
   end
 end