diff --git a/.mocha.env b/.mocha.env
new file mode 100644
index 00000000..78a9f930
--- /dev/null
+++ b/.mocha.env
@@ -0,0 +1 @@
+NODE_PATH=./out
diff --git a/.mocharc.yml b/.mocharc.yml
new file mode 100644
index 00000000..c19fe15a
--- /dev/null
+++ b/.mocharc.yml
@@ -0,0 +1,11 @@
+require:
+  - source-map-support/register
+spec:
+  - out/**/*.test.js
+  - addons/**/out/*.test.js
+watch-files:
+  - out/**/*.js
+  - addons/**/out/*.js
+reporter: spec
+color: true
+check-leaks: true
diff --git a/.vscode/settings.json b/.vscode/settings.json
index f07ca545..9fa94d5f 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,4 +1,5 @@
 {
     "typescript.preferences.importModuleSpecifier": "non-relative",
-    "typescript.preferences.quoteStyle": "single"
+    "typescript.preferences.quoteStyle": "single",
+    "mochaExplorer.envPath": ".mocha.env"
 }
diff --git a/package.json b/package.json
index 71a0f308..29b6fd46 100644
--- a/package.json
+++ b/package.json
@@ -23,6 +23,7 @@
     "test-api-webkit": "node ./bin/test_api.js --browser=webkit --timeout=20000",
     "test-unit": "node ./bin/test.js",
     "test-unit-coverage": "node ./bin/test.js --coverage",
+    "test-unit-dev": "cross-env NODE_PATH='./out' mocha",
     "build": "tsc -b ./tsconfig.all.json",
     "prepare": "npm run setup",
     "setup": "npm run build",
@@ -49,6 +50,7 @@
     "@typescript-eslint/eslint-plugin": "^4.23.0",
     "@typescript-eslint/parser": "^4.23.0",
     "chai": "^4.3.4",
+    "cross-env": "^7.0.3",
     "deep-equal": "^2.0.5",
     "eslint": "^7.26.0",
     "express": "^4.17.1",
@@ -61,6 +63,7 @@
     "nyc": "^15.1.0",
     "playwright": "^1.11.0",
     "source-map-loader": "^2.0.1",
+    "source-map-support": "^0.5.19",
     "ts-loader": "^9.1.2",
     "typescript": "^4.2.4",
     "utf8": "^3.0.0",
diff --git a/yarn.lock b/yarn.lock
index 571f8a90..cf92d8f7 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -1329,7 +1329,14 @@ core-util-is@1.0.2, core-util-is@~1.0.0:
   resolved "https://registry.yarnpkg.com/core-util-is/-/core-util-is-1.0.2.tgz#b5fd54220aa2bc5ab57aab7140c940754503c1a7"
   integrity sha1-tf1UIgqivFq1eqtxQMlAdUUDwac=
 
-cross-spawn@^7.0.0, cross-spawn@^7.0.2, cross-spawn@^7.0.3:
+cross-env@^7.0.3:
+  version "7.0.3"
+  resolved "https://registry.yarnpkg.com/cross-env/-/cross-env-7.0.3.tgz#865264b29677dc015ba8418918965dd232fc54cf"
+  integrity sha512-+/HKd6EgcQCJGh2PSjZuUitQBQynKor4wrFbRg4DtAgS1aWO+gU52xpH7M9ScGgXSYmAVS9bIJ8EzuaGw0oNAw==
+  dependencies:
+    cross-spawn "^7.0.1"
+
+cross-spawn@^7.0.0, cross-spawn@^7.0.1, cross-spawn@^7.0.2, cross-spawn@^7.0.3:
   version "7.0.3"
   resolved "https://registry.yarnpkg.com/cross-spawn/-/cross-spawn-7.0.3.tgz#f73a85b9d5d41d045551c177e2882d4ac85728a6"
   integrity sha512-iRDPJKUPVEND7dHPO8rkbOnPpyDygcDFtWjpeWNCgy8WP2rXcxXL8TskReQl6OrB2G7+UJrags1q15Fudc7G6w==
@@ -3909,7 +3916,7 @@ source-map-loader@^2.0.1:
     iconv-lite "^0.6.2"
     source-map-js "^0.6.2"
 
-source-map-support@~0.5.19:
+source-map-support@^0.5.19, source-map-support@~0.5.19:
   version "0.5.19"
   resolved "https://registry.yarnpkg.com/source-map-support/-/source-map-support-0.5.19.tgz#a98b62f86dcaf4f67399648c085291ab9e8fed61"
   integrity sha512-Wonm7zOCIJzBGQdB+thsPar0kYuCIzYvxZwlBa87yi/Mdjv7Tip2cyVbLj5o0cFPN4EVkuTwb3GDDyUx2DGnGw==