fix(config): force default output.filename (#477)

this prevents karma-webpack from failing and also
prints out a useful error message explaining why
the webpack output.filename is ignored.

Fixes N/A

lib/karma-webpack/controller.js

@@ -21,6 +21,16 @@ class KW_Controller {
   }
 
   updateWebpackOptions(newOptions) {
+    if (newOptions.output && newOptions.output.filename) {
+      console.warn(
+        `
+karma-webpack does not currently support customized filenames via
+webpack output.filename, if this is something you need consider opening a ticket.
+defaulting ${newOptions.output.filename} to file[id].`.trim()
+      );
+      delete newOptions.output.filename;
+    }
+
     this.webpackOptions = merge(this.webpackOptions, newOptions);
   }
 

test/integration/scenarios/basic-setup/custom-output-path.test.js

@@ -0,0 +1,84 @@
+/* eslint-disable prettier/prettier */
+
+import karmaChromeLauncher from 'karma-chrome-launcher';
+import karmaMocha from 'karma-mocha';
+import karmaChai from 'karma-chai';
+
+import Scenario from '../../utils/scenario';
+
+const fs = require('fs');
+
+process.env.CHROME_BIN = require('puppeteer').executablePath();
+
+const path = require('path');
+
+const karmaWebpack = require('../../../../lib/index');
+
+// The karma server integration tests take longer than the jest 5 sec default,
+// we will give them 30 seconds to complete.
+const KARMA_SERVER_TIMEOUT = 30 * 1000;
+const KARMA_CUSTOM_PATH = '/tmp/karma_webpack__custom_file_path';
+
+describe('A basic karma-webpack setup', () => {
+  let scenario;
+
+  const TEST_PATH = path.resolve(__dirname, './index.scenario.js');
+
+  const config = {
+    frameworks: ['mocha', 'chai', 'webpack'],
+    files: [{ pattern: TEST_PATH }],
+    preprocessors: { [TEST_PATH]: ['webpack'] },
+    webpack: {
+      devtool: false,
+      output: {
+        path: KARMA_CUSTOM_PATH,
+        filename: 'hi_[id].js',
+      }
+    },
+    browsers: ['ChromeHeadless'],
+    // Explicitly turn off reporters so the simulated test results are not confused with the actual results.
+    reporters: [],
+    plugins: [karmaWebpack, karmaChromeLauncher, karmaMocha, karmaChai],
+    port: 2389,
+    logLevel: 'ERROR',
+    singleRun: true
+  };
+
+  beforeAll((done) => {
+    Scenario.run(config)
+      .then((res) => {
+        scenario = res;
+      })
+      .catch((err) => console.error('Integration Scenario Failed: ', err))
+      .finally(() => done());
+  }, KARMA_SERVER_TIMEOUT);
+
+  it('should have an exit code of 1 because it contains a failing test', () => {
+    expect(scenario.exitCode).toBe(1);
+  })
+
+  it('should have three successful test runs', () => {
+    expect(scenario.success).toBe(3);
+  });
+
+  it('should have one failed test run', () => {
+    expect(scenario.failed).toBe(1);
+  });
+
+  it('should complete with no errors', () => {
+    expect(scenario.error).toBe(false);
+  });
+
+  it('should create the custom karma_webpack__custom_file_path directory', () => {
+    expect(fs.existsSync(KARMA_CUSTOM_PATH)).toBe(true);
+  })
+
+  it('should contain the generated commons file', () => {
+    expect(fs.existsSync(`${KARMA_CUSTOM_PATH}/commons.js`)).toBe(true)
+  })
+
+  it('should contain the generated runtime file', () => {
+    expect(fs.existsSync(`${KARMA_CUSTOM_PATH}/runtime.js`)).toBe(true)
+  })
+
+});