refactor: move jest around and add code coverage

ci/dev/postinstall.sh

@@ -5,6 +5,11 @@ main() {
   cd "$(dirname "$0")/../.."
   source ./ci/lib.sh
 
+  # This installs the dependencies needed for testing
+  cd test
+  yarn
+  cd ..
+
   cd lib/vscode
   yarn ${CI+--frozen-lockfile}