Minimal showcase for TypeStrong/ts-loader/issues/919

.gitignore

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+node_modules/
+

package.json

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+{
+  "private": true,
+  "name": "ts-loader-minimal-jest-failure",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "devDependencies": {
+    "@types/jest": "^24.0.12",
+    "@types/webpack": "^4.4.31",
+    "jest": "^24.8.0",
+    "ts-loader": "6",
+    "typescript": "^3.4.5",
+    "webpack": "^4.31.0",
+    "webpack-cli": "^3.3.2",
+    "webpack-dev-server": "^3.3.1"
+  }
+}

src/index.test.ts

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+import { foo } from ".";
+
+test('test foo', () => {
+    expect(foo()).toBeUndefined()
+})

src/index.ts

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+export function foo() {
+    return undefined
+}

tsconfig.json

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+{
+  "compilerOptions": {
+    "target": "es2017",
+    "module": "esnext",
+    "outDir": "./dist",
+    "rootDir": "./",
+    "strict": true,
+    "moduleResolution": "node",
+    "esModuleInterop": true
+  }
+}

webpack.config.js

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+// @ts-check
+/** @typedef {import('webpack').Configuration} Configuration */
+
+const path = require('path');
+
+/** @type Configuration */
+module.exports = {
+    mode: 'development',
+    entry: './src/index',
+    output: {
+        path: path.join(__dirname, 'dist'),
+        filename: 'bundle.js'
+    },
+    resolve: {
+        extensions: ['.tsx', '.ts', '.js']
+    },
+    module: {
+        rules: [{
+            test: /\.tsx?$/,
+            use: 'ts-loader'
+        }]
+    }
+}