Issue #3438070 by berdir, catch, bbrala: Add JSON:API performance tests

Issue #3418184 by nikolay shapovalov, smustgrave, larowlan, quietone:…

Issue #3004425 by dgilbert, krzysztof domański, codebymikey, avpadern…

Issue #3508308 by bbrala, borisson_: Validate system.action.*: add ne…

Issue #3514924 by mstrelan: [random test failure] JSWebAssertTest::te…

Issue #3281955 by prudloff: Add a way to debug big_pipe cache tags

Issue #3513875 by mstrelan: Move test middleware out of CoreServicePr…

Issue #3514226 by mstrelan, smustgrave: Add void return to functions …

Issue #3387939 by mstrelan, catch: [random test failure] ToolbarClaro…

Issue #3511782 by quietone: Fix TestSiteInstallCommand to not rely on…

Issue #3260219 by trackleft2, smustgrave, joegraduate, mikelutz: Allo…

Issue #3260219 by trackleft2, smustgrave, joegraduate, mikelutz: Allo…

Issue #3347015 by acbramley, dieterholvoet, smustgrave, gábor hojtsy,…

Issue #3223211 by acbramley, catch: Deprecate node_mark

Issue #3514235 by mstrelan, smustgrave: Add array return to functions…

Issue #3508649 by gábor hojtsy, smustgrave: Use Drupal Core Leadershi…

Issue #3508649 by gábor hojtsy, smustgrave: Use Drupal Core Leadershi…

Issue #3508649 by gábor hojtsy, smustgrave: Use Drupal Core Leadershi…

Issue #3508649 by gábor hojtsy, smustgrave: Use Drupal Core Leadershi…

Issue #3514904 by mstrelan, acbramley: [consistent test failure] Asse…

Issue #3389994 by mstrelan, quietone: [random test failure] MediaTest…

Issue #3400150 by mstrelan, quietone: [random test failure] Timestamp…

Issue #3512284 by catch, jacine, feuerwagen: Remove details.css since…

Issue #3497341 by berdir: Add caching to ConfigurableLanguageManager:…

Issue #3507866 by plopesc, m4olivei, ckrina, berdir, catch: Enable th…

Issue #3510939 by mikelutz, balazswmann, godotislate, mxr576: Avoid r…

Issue #3508506 by quietone, smustgrave, borisson_: Fix Drupal.Comment…

Issue #3513317 by annmarysruthy, larowlan, wim leers: ImageItem::defa…

Issue #3513317 by annmarysruthy, larowlan, wim leers: ImageItem::defa…

Issue #3513317 by annmarysruthy, larowlan, wim leers: ImageItem::defa…