fix: Fix incorrect rootPath resolution in jest plugin (#833)

Author: tryggvigy

packages/knip/fixtures/plugins/jest2/jest.config.js

@@ -0,0 +1,3 @@
+module.exports = {
+  displayName: 'dev',
+};

packages/knip/fixtures/plugins/jest2/knip.ts

@@ -0,0 +1,13 @@
+export default {
+  "jest": {
+    "config": [
+      "jest.config.js",
+      "project1/jest.config.js",
+      "package.json"
+    ],
+    "entry": [
+      "**/__tests__/**/*.[jt]s?(x)",
+      "**/?(*.)+(spec|test).[jt]s?(x)"
+    ]
+  }
+}

packages/knip/fixtures/plugins/jest2/package.json

@@ -0,0 +1,8 @@
+{
+  "name": "@fixtures/jest2",
+  "scripts": {},
+  "devDependencies": {
+    "jest": "*",
+    "@testing-library/jest-dom": "*"
+  }
+}

packages/knip/fixtures/plugins/jest2/project1/jest.config.js

@@ -0,0 +1,7 @@
+const path = require('path');
+
+module.exports = {
+  rootDir: path.join(__dirname, '../'),
+  displayName: 'project1',
+  setupFilesAfterEnv: ['<rootDir>/project1/setupFiles/setup.js'],
+};

packages/knip/fixtures/plugins/jest2/project1/setupFiles/setup.js

@@ -0,0 +1 @@
+import '@testing-library/jest-dom/extend-expect';

packages/knip/src/plugins/jest/index.ts

@@ -112,16 +112,15 @@ const resolveDependencies = async (config: JestInitialOptions, options: PluginOp
 const resolveEntryPaths: ResolveEntryPaths<JestConfig> = async (localConfig, options) => {
   const { configFileDir } = options;
   if (typeof localConfig === 'function') localConfig = await localConfig();
-  const rootDir = localConfig.rootDir ? join(configFileDir, localConfig.rootDir) : configFileDir;
+  const rootDir = localConfig.rootDir ?? configFileDir;
   const replaceRootDir = (name: string) => name.replace(/<rootDir>/, rootDir);
   return (localConfig.testMatch ?? []).map(replaceRootDir).map(toEntry);
 };
 
 const resolveConfig: ResolveConfig<JestConfig> = async (localConfig, options) => {
   const { configFileDir } = options;
   if (typeof localConfig === 'function') localConfig = await localConfig();
-  const rootDir = localConfig.rootDir ? join(configFileDir, localConfig.rootDir) : configFileDir;
-
+  const rootDir = localConfig.rootDir ?? configFileDir;
   const replaceRootDir = (name: string) => name.replace(/<rootDir>/, rootDir);
 
   const inputs = await resolveDependencies(localConfig, options);

packages/knip/test/plugins/jest2.test.ts

@@ -0,0 +1,31 @@
+import { test } from 'bun:test';
+import assert from 'node:assert/strict';
+import { main } from '../../src/index.js';
+import { join, resolve } from '../../src/util/path.js';
+import baseArguments from '../helpers/baseArguments.js';
+import baseCounters from '../helpers/baseCounters.js';
+
+const cwd = resolve('fixtures/plugins/jest2');
+
+test('Find dependencies with the Jest plugin', async () => {
+  const { issues, counters } = await main({
+    ...baseArguments,
+    cwd,
+  });
+
+  assert(issues.devDependencies['package.json']['jest']);
+
+  // Correctly identifies setup file in a non-root jest.config.js which uses
+  // <rootDir> to reference the root directory.
+  assert(!issues.files.has(join(cwd, 'project1/setupFiles/setup.js')));
+
+  assert.deepEqual(counters, {
+    ...baseCounters,
+    files: 0,
+    devDependencies: 1,
+    unlisted: 0,
+    unresolved: 0,
+    processed: 4,
+    total: 4,
+  });
+});