Add source maps to the test build

This way, if a test assertion fails, we know what line of code the
assertion was originally on

package.json

@@ -5,7 +5,7 @@
   "license": "MIT",
   "scripts": {
     "build": "webpack",
-    "test": "TESTBUILD=true webpack && mocha test-dist/main.js && rm -rf test-dist"
+    "test": "TESTBUILD=true webpack && mocha test-dist/main.js --require source-map-support/register && rm -rf test-dist"
   },
   "devDependencies": {
     "babel-core": "^6.26.3",
@@ -14,6 +14,7 @@
     "chai": "^4.2.0",
     "jquery": "^3.3.1",
     "mocha": "^5.2.0",
+    "source-map-support": "^0.5.9",
     "webpack": "^4.28.2",
     "webpack-cli": "^3.1.2"
   }

webpack.config.js

@@ -2,9 +2,11 @@ let glob = require("glob");
 
 let entry = __dirname + "/app/src/page.js";
 let outputPath = __dirname + "/dist/";
+let devtool = "";
 if (process.env.TESTBUILD) {
   entry = glob.sync(__dirname + "/app/test/**/*.test.js");
   outputPath = __dirname + "/test-dist/";
+  devtool = "source-map";
 }
 
 module.exports = {
@@ -28,4 +30,5 @@ module.exports = {
       },
     ],
   },
+  devtool: devtool,
 };

yarn.lock

@@ -3178,7 +3178,7 @@ source-map-support@^0.4.15:
   dependencies:
     source-map "^0.5.6"
 
-source-map-support@~0.5.6:
+source-map-support@^0.5.9, source-map-support@~0.5.6:
   version "0.5.9"
   resolved "https://registry.yarnpkg.com/source-map-support/-/source-map-support-0.5.9.tgz#41bc953b2534267ea2d605bccfa7bfa3111ced5f"
   integrity sha512-gR6Rw4MvUlYy83vP0vxoVNzM6t8MUXqNuRsuBmBHQDu1Fh6X015FrLdgoDKcNdkwGubozq0P4N0Q37UyFVr1EA==