Normalize handling of test build and run

scripts/travis_script.sh

@@ -14,6 +14,7 @@ if [[ $GROUP == tests ]]; then
     # Run the JS and python tests
     py.test
     npm run build
+    npm run build:test
     npm test
 
     # Make sure we have CSS that can be converted with postcss
@@ -34,6 +35,7 @@ fi
 if [[ $GROUP == coverage ]]; then
     # Run the coverage check.
     npm run build
+    npm run build:test
     npm run coverage
 
     # Run the link check

test/package.json

@@ -2,7 +2,7 @@
   "private": true,
   "name": "@jupyterlab/test-all",
   "scripts": {
-    "build": "tsc && webpack",
+    "build:test": "tsc && webpack",
     "coverage": "webpack --config webpack-cov.conf.js && python run-test.py karma-cov.conf.js",
     "test": "npm run test:firefox",
     "test:chrome": "python run-test.py --browsers=Chrome karma.conf.js",