Add --build-only parameter to filter build outputs

Also, don't generate test bundle by default, but provide
`npm run build-test` instead.

package.json

@@ -27,9 +27,11 @@
   ],
   "scripts": {
     "build": "rollup --config",
+    "build-test": "npm run build --build-only=test",
     "prepare": "npm run build",
     "test": "mocha --timeout 120000 test/unittests.js",
     "start": "http-server",
+    "prebrowsertest": "npm run build-test",
     "browsertest": "npm start -- -o test/unittests.html",
     "coverage": "nyc npm test",
     "lint": "eslint 'src/**/*.js' 'test/crypto/**/*.js'",

rollup.config.js

@@ -23,7 +23,7 @@ const terserOptions = {
   }
 };
 
-export default [
+export default Object.assign([
   {
     input: 'src/index.js',
     output: [
@@ -100,4 +100,14 @@ export default [
       })
     ]
   }
-];
+].filter(config => {
+  config.output = config.output.filter(output => {
+    return (output.file || output.dir + '/' + output.entryFileNames).includes(
+      process.env.npm_config_build_only || // E.g. `npm install --build-only=lightweight`.
+      'dist' // Don't build test bundle by default.
+    );
+  });
+  return config.output.length;
+}), {
+  allow_empty: true // Fake option to trick rollup into accepting empty config array when filtered above.
+});

travis.sh

@@ -14,6 +14,7 @@ elif [ $OPENPGPJSTEST = "unit" ]; then
 elif [ $OPENPGPJSTEST = "browserstack" ]; then
   echo "Running OpenPGP.js browser unit tests on Browserstack."
 
+  npm run build-test
   echo -n "Using config: "
   echo "{\"browsers\": [$BROWSER], \"test_framework\": \"mocha\", \"test_path\": [\"test/unittests.html?ci=true${LIGHTWEIGHT+&lightweight=true&grep=lightweight}\"], \"timeout\": 1800, \"exit_with_fail\": true, \"project\": \"openpgpjs/${TRAVIS_EVENT_TYPE:-push}${LIGHTWEIGHT:+/lightweight}\"}" > browserstack.json
   cat browserstack.json