Add tests to ensure we don't interfere with json gem's output

1 files changed, 52 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/object/json_gem_encoding_test.rb b/activesupport/test/core_ext/object/json_gem_encoding_test.rb
new file mode 100644
index 0000000000..4368e3e1d6
--- /dev/null
+++ b/activesupport/test/core_ext/object/json_gem_encoding_test.rb
@@ -0,0 +1,52 @@
+require 'abstract_unit'
+require 'json'
+require 'json/encoding_test_cases'
+
+# These test cases were added to test that we do not interfere with json gem's
+# output when the AS encoder is loaded, primarily for problems reported in
+# #20775. They need to be executed in isolation to reproduce the scenario
+# correctly, because other test cases might have already loaded additional
+# dependencies.
+
+# The AS::JSON encoder requires the BigDecimal core_ext, which, unfortunately,
+# changes the BigDecimal#to_s output, and consequently the JSON gem output. So
+# we need to require this unfront to ensure we don't get a false failure, but
+# ideally we should just fix the BigDecimal core_ext to not change to_s without
+# arguments.
+require 'active_support/core_ext/big_decimal'
+
+class JsonGemEncodingTest < ActiveSupport::TestCase
+  include ActiveSupport::Testing::Isolation
+
+  JSONTest::EncodingTestCases.constants.each_with_index do |name|
+    JSONTest::EncodingTestCases.const_get(name).each_with_index do |(subject, _), i|
+      test("test #{name[0..-6].underscore} #{i}") do
+        begin
+          expected = JSON.generate(subject, quirks_mode: true)
+        rescue JSON::GeneratorError => e
+          exception = e
+        end
+
+        require_or_skip 'active_support/core_ext/object/json'
+
+        if exception
+          assert_raises_with_message JSON::GeneratorError, e.message do
+            JSON.generate(subject, quirks_mode: true)
+          end
+        else
+          assert_equal expected, JSON.generate(subject, quirks_mode: true)
+        end
+      end
+    end
+  end
+
+  private
+    def require_or_skip(file)
+      require(file) || skip("'#{file}' was already loaded")
+    end
+
+    def assert_raises_with_message(exception_class, message, &block)
+      err = assert_raises(exception_class) { block.call }
+      assert_match message, err.message
+    end
+end