diff --git a/.gitignore b/.gitignore
index 08c992e..376a272 100644
--- a/.gitignore
+++ b/.gitignore
@@ -3,3 +3,5 @@ build/
 package-lock.json
 yarn.lock
 public
+coverage
+ckeditor5/
\ No newline at end of file
diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 0000000..7a73a41
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,2 @@
+{
+}
\ No newline at end of file
diff --git a/README.md b/README.md
index 8811631..110a0ed 100644
--- a/README.md
+++ b/README.md
@@ -230,3 +230,8 @@ To enter a development loop with hot reload support:
 -   http://localhost:8080
 
 [ckeditor 5 inspector]: https://ckeditor.com/docs/ckeditor5/latest/framework/guides/development-tools.html#ckeditor-5-inspector
+
+### Tests
+
+To run tests, use `yarn test`, optionally with `--coverage`, `--watch`, or `--source-map`, to run tests.
+You will need to have run `git submodule init` and `git submodule update` first.
diff --git a/package.json b/package.json
index f2db2a3..37afda9 100644
--- a/package.json
+++ b/package.json
@@ -23,21 +23,23 @@
   "devDependencies": {
     "@ckeditor/ckeditor5-basic-styles": "^27.1.0",
     "@ckeditor/ckeditor5-dev-tests": "^24.4.2",
+    "@ckeditor/ckeditor5-dev-webpack-plugin": "^24.4.2",
     "@ckeditor/ckeditor5-editor-inline": "^27.1.0",
     "@ckeditor/ckeditor5-essentials": "^27.1.0",
     "@ckeditor/ckeditor5-paragraph": "^27.1.0",
     "@ckeditor/ckeditor5-theme-lark": "^27.1.0",
-    "css-loader": "^5.2.4",
+    "css-loader": "4",
     "eslint": "^7.1.0",
     "eslint-config-ckeditor5": "^3.1.0",
-    "html-webpack-plugin": "^5.3.1",
+    "html-webpack-plugin": "4",
     "husky": "^4.2.5",
+    "karma-webpack": "^4.0.2",
     "lint-staged": "^10.2.6",
     "mini-css-extract-plugin": "^1.6.0",
     "raw-loader": "^4.0.2",
     "stylelint": "^13.5.0",
     "stylelint-config-ckeditor5": "^2.0.1",
-    "webpack": "^5.36.2",
+    "webpack": "^4.43.0",
     "webpack-cli": "^4.6.0",
     "webpack-dev-server": "^3.11.2"
   },
@@ -61,7 +63,8 @@
     "lint": "eslint --quiet src/**/*.js",
     "lint:fix": "eslint --quiet src/**/*.js --fix",
     "stylelint": "stylelint --quiet --allow-empty-input 'theme/**/*.css' 'docs/**/*.css'",
-    "test": "node node_modules/@ckeditor/ckeditor5-dev-tests/bin/test.js",
+    "pretest": "bash -c 'if [ ! -e node_modules/@ckeditor/ckeditor5-core/tests/_utils ]; then git clone --no-checkout --depth=1 --filter=blob:none https://github.com/ckeditor/ckeditor5 && git -C ckeditor5 sparse-checkout set packages/ckeditor5-core packages/ckeditor5-core/tests/_utils && git -C ckeditor5 checkout master && ln -sfrT ckeditor5/packages/ckeditor5-core/tests node_modules/@ckeditor/ckeditor5-core/tests ; fi'",
+    "test": "node node_modules/.bin/ckeditor5-dev-tests --files=ckeditor5",
     "start": "node node_modules/.bin/webpack serve --mode development"
   },
   "lint-staged": {