diff --git a/.prettierrc.json b/.prettierrc.json
new file mode 100644
index 0000000..544138b
--- /dev/null
+++ b/.prettierrc.json
@@ -0,0 +1,3 @@
+{
+  "singleQuote": true
+}
diff --git a/constants.js b/constants.js
new file mode 100644
index 0000000..196841c
--- /dev/null
+++ b/constants.js
@@ -0,0 +1,7 @@
+// Empty extension takes advantage of Node's default require behavior to check for
+// eslint-local-rules.js as well as an eslint-local-rules folder with an index.js
+var DEFAULT_EXTENSIONS = ['', '.cjs'];
+
+module.exports = {
+  DEFAULT_EXTENSIONS,
+};
diff --git a/fixtures/projectWithBadImport/eslint-local-rules.js b/fixtures/projectWithBadImport/eslint-local-rules.js
new file mode 100644
index 0000000..9b49287
--- /dev/null
+++ b/fixtures/projectWithBadImport/eslint-local-rules.js
@@ -0,0 +1,3 @@
+require('./does-not-exist');
+
+module.exports = {};
diff --git a/fixtures/projectWithResolution/eslint-local-rules.js b/fixtures/projectWithResolution/eslint-local-rules.js
new file mode 100644
index 0000000..f053ebf
--- /dev/null
+++ b/fixtures/projectWithResolution/eslint-local-rules.js
@@ -0,0 +1 @@
+module.exports = {};
diff --git a/fixtures/projectWithResolutionCjs/eslint-local-rules.cjs b/fixtures/projectWithResolutionCjs/eslint-local-rules.cjs
new file mode 100644
index 0000000..f053ebf
--- /dev/null
+++ b/fixtures/projectWithResolutionCjs/eslint-local-rules.cjs
@@ -0,0 +1 @@
+module.exports = {};
diff --git a/fixtures/projectWithResolutionIndex/eslint-local-rules/index.js b/fixtures/projectWithResolutionIndex/eslint-local-rules/index.js
new file mode 100644
index 0000000..f053ebf
--- /dev/null
+++ b/fixtures/projectWithResolutionIndex/eslint-local-rules/index.js
@@ -0,0 +1 @@
+module.exports = {};
diff --git a/index.js b/index.js
index 2380ca0..a5d348a 100644
--- a/index.js
+++ b/index.js
@@ -1,46 +1,23 @@
 /* eslint-env node */
 'use strict';
 
-var path = require('path');
+var { requireUp } = require('./requireUp');
+var { DEFAULT_EXTENSIONS } = require('./constants');
 
-// Empty extension takes advantage of Node's default require behavior to check for
-// eslint-local-rules.js as well as an eslint-local-rules folder with an index.js
-var exts = ['', '.cjs'];
-var rules = requireUp('eslint-local-rules', __dirname);
+var rules = requireUp('eslint-local-rules', DEFAULT_EXTENSIONS, __dirname);
 
 if (!rules) {
   throw new Error(
     'eslint-plugin-local-rules: ' +
-    'Cannot find "eslint-local-rules{' + ['.js'].concat(exts.filter(Boolean)) + "} " +
-    'or eslint-local-rules/index.js (checked all ancestors of "' + __dirname + '").'
+      'Cannot find "eslint-local-rules{' +
+      ['.js'].concat(exts.filter(Boolean)) +
+      '} ' +
+      'or eslint-local-rules/index.js (checked all ancestors of "' +
+      __dirname +
+      '").'
   );
 }
 
 module.exports = {
   rules: rules,
 };
-
-// Attempt to require a file, recursively checking parent directories until found
-// Similar to native `require` behavior, but doesn't check in `node_modules` folders
-// Based on https://github.com/js-cli/node-findup-sync
-function requireUp(filename, cwd) {
-  var filepath = path.resolve(cwd, filename);
-
-  for (var i = 0; i < exts.length; i++) {
-    try {
-      return require(filepath + exts[i]);
-    } catch(error) {
-      // Ignore OS errors (will recurse to parent directory)
-      if (error.code !== 'MODULE_NOT_FOUND') {
-        throw error;
-      }
-    }
-  }
-
-  var dir = path.dirname(cwd);
-  if (dir === cwd) {
-    return undefined;
-  }
-
-  return requireUp(filename, dir);
-}
diff --git a/package.json b/package.json
index def5b2f..5af3de4 100644
--- a/package.json
+++ b/package.json
@@ -4,7 +4,7 @@
   "description": "A plugin for ESLint that allows you to use project-specific rules",
   "main": "index.js",
   "scripts": {
-    "test": "echo \"Error: no test specified\" && exit 1"
+    "test": "vitest"
   },
   "repository": {
     "type": "git",
@@ -19,5 +19,9 @@
   "bugs": {
     "url": "https://github.com/cletusw/eslint-plugin-local-rules/issues"
   },
-  "homepage": "https://github.com/cletusw/eslint-plugin-local-rules#readme"
+  "homepage": "https://github.com/cletusw/eslint-plugin-local-rules#readme",
+  "devDependencies": {
+    "prettier": "2.6.2",
+    "vitest": "^0.14.2"
+  }
 }
diff --git a/requireUp.js b/requireUp.js
new file mode 100644
index 0000000..dafb9c0
--- /dev/null
+++ b/requireUp.js
@@ -0,0 +1,38 @@
+var path = require('path');
+
+/**
+ * Attempt to require a file, recursively checking parent directories until found.
+ * Similar to native `require` behavior, but doesn't check in `node_modules` folders.
+ * Based on https://github.com/js-cli/node-findup-sync.
+ *
+ * @param filename {string} The name of the target file
+ * @param exts {string[]} The file extensions to look for (e.g. '.cjs')
+ * @param cwd {string} The directory to search in
+ */
+function requireUp(filename, exts, cwd) {
+  for (var i = 0; i < exts.length; i++) {
+    var filepath = path.resolve(cwd, filename) + exts[i];
+    try {
+      return require(filepath);
+    } catch (error) {
+      var filepathNotFound =
+        error.code === 'MODULE_NOT_FOUND' &&
+        error.message.includes(`Cannot find module '${filepath}'`);
+
+      // Rethrow unless error is just saying `filepath` not found (in that case,
+      // let next loop check parent directory instead).
+      if (!filepathNotFound) {
+        throw error;
+      }
+    }
+  }
+  var dir = path.dirname(cwd);
+  if (dir === cwd) {
+    return undefined;
+  }
+  return requireUp(filename, exts, dir);
+}
+
+module.exports = {
+  requireUp,
+};
diff --git a/requireUp.test.js b/requireUp.test.js
new file mode 100644
index 0000000..c697815
--- /dev/null
+++ b/requireUp.test.js
@@ -0,0 +1,59 @@
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { describe, it, expect } from 'vitest';
+
+import { requireUp } from './requireUp';
+import { DEFAULT_EXTENSIONS } from './constants';
+
+const __dirname = path.dirname(fileURLToPath(import.meta.url));
+
+// Path to the 'fixtures' directory
+const fixturesDir = path.resolve(__dirname, './fixtures');
+
+describe('requireUp', () => {
+  it('should find the file at eslint-local-rules.js', () => {
+    const file = requireUp(
+      'eslint-local-rules',
+      DEFAULT_EXTENSIONS,
+      path.join(fixturesDir, './projectWithResolution/a')
+    );
+    expect(file).toBeDefined();
+  });
+
+  it('should find the file at eslint-local-rules.cjs', () => {
+    const file = requireUp(
+      'eslint-local-rules',
+      DEFAULT_EXTENSIONS,
+      path.join(fixturesDir, './projectWithResolutionCjs/a')
+    );
+    expect(file).toBeDefined();
+  });
+
+  it('should find the file at eslint-local-rules/index.js', () => {
+    const file = requireUp(
+      'eslint-local-rules',
+      DEFAULT_EXTENSIONS,
+      path.join(fixturesDir, './projectWithResolutionIndex/a')
+    );
+    expect(file).toBeDefined();
+  });
+
+  it('should fail to find a file that does not exist', () => {
+    const file = requireUp(
+      'some-file-that-will-not-resolve',
+      DEFAULT_EXTENSIONS,
+      path.join(fixturesDir, './projectWithNoResolution/a')
+    );
+    expect(file).not.toBeDefined();
+  });
+
+  it('should throw MODULE_NOT_FOUND errors for modules other than the target', () => {
+    expect(() => {
+      requireUp(
+        'eslint-local-rules',
+        DEFAULT_EXTENSIONS,
+        path.join(fixturesDir, './projectWithBadImport/a')
+      );
+    }).toThrowError(`Cannot find module './does-not-exist'`);
+  });
+});