Fix `ActionDispatch::IntegrationTest#open_session`

Reset a new session directly after its creation in
`ActionDispatch::IntegrationTest#open_session`. Reset the session to a clean
state before making it available to the client's test code.

Issue #22742 reports unexpected behavior of integration tests that run multiple
sessions. For example an `ActionDispatch::Flash` instance is shared across
multiple sessions, though a client code will rightfully assume that each new
session has its own flash hash.

The following test failed due to this behavior:

    class Issue22742Test < ActionDispatch::IntegrationTest
      test 'issue #22742' do
        integration_session # initialize first session
        a = open_session
        b = open_session

        refute_same(a.integration_session, b.integration_session)
      end
    end

Instead of creating a new `ActionDispatch::Integration::Session` instance,
the same instance is shared across all newly opened test sessions. This is
due to the way how new test sessions are created in
`ActionDispatch::IntegrationTest#open_session`. The already existing
`ActionDispatch::IntegrationTest` instance is duplicated  with `Object#dup`,
This approach was introduced in commit 15c31c7639b. `Object#dup` copies the
instance variables, but not the objects they reference. Therefore this issue
only occurred when the current test instance had been tapped in such a way that
the instance variable `@integration_session` was initialized before creating the
new test session.

Close #22742

[Tawan Sierek + Sina Sadeghian]

1 files changed, 6 insertions, 0 deletions

diff --git a/railties/CHANGELOG.md b/railties/CHANGELOG.md
index 7db7e2e34d..049a06db3a 100644
--- a/railties/CHANGELOG.md
+++ b/railties/CHANGELOG.md
@@ -1,3 +1,9 @@
+*   Reset a new session directly after its creation in ActionDispatch::IntegrationTest#open_session
+
+    Fixes Issue #22742
+
+    *Tawan Sierek*
+
 *   Add `:skip_sprockets` to `Rails::PluginBuilder::PASSTHROUGH_OPTIONS`
 
     *Tsukuru Tanimichi*