Use custom directory when installing dependent extensions

To avoid interference pf the testing code with existing extensions
and to make sure that the VSCode has only necessary extensions installed for test run

src/test/runTest.ts

@@ -25,8 +25,11 @@ async function main() {
       'jcanero.hoogle-vscode',
       'dramforever.vscode-ghc-simple'
     ];
+
+    const extensionsDir = path.resolve(path.dirname(cliPath), '..', 'extensions');
+
     for(const extension of dependencies) {
-      cp.spawnSync(cliPath, ['--install-extension', extension], {
+      cp.spawnSync(cliPath, ['--extensions-dir', extensionsDir, '--install-extension', extension], {
         encoding: 'utf-8',
         stdio: 'inherit'
       });
@@ -41,6 +44,7 @@ async function main() {
         '--new-window',
         '--disable-gpu',
         '--disable-updates',
+        '--extensions-dir', extensionsDir,
         '--logExtensionHostCommunication',
         '--skip-getting-started',
         '--skip-release-notes',