test: cover conditions with unit tests

src/utils.ts

@@ -1,6 +1,9 @@
 import * as fs from 'fs';
 import * as path from 'path';
 
+/**
+ * Extracts the file name from handler string.
+ */
 export function extractFileName(cwd: string, handler: string): string {
   const fnName = path.extname(handler);
   const fnNameLastAppearanceIndex = handler.lastIndexOf(fnName);
@@ -40,7 +43,10 @@ export function findUp(name: string, directory: string = process.cwd()): string
   return findUp(name, path.dirname(absoluteDirectory));
 }
 
-export function findProjectRoot(rootDir: string): string {
+/**
+ * Forwards `rootDir` or finds project root folder.
+ */
+export function findProjectRoot(rootDir?: string): string | undefined {
   return rootDir
     ?? findUp(`.git${path.sep}`)
     ?? findUp('yarn.lock')

tests/index.test.ts

@@ -2,32 +2,84 @@ jest.mock('esbuild');
 
 import '@aws-cdk/assert/jest';
 
+import { Runtime, RuntimeFamily } from '@aws-cdk/aws-lambda';
 import { Stack } from '@aws-cdk/core';
 import { buildSync } from 'esbuild';
 import mockfs from 'mock-fs';
+import path from 'path';
 
 import { NodejsFunction } from '../src';
 
+
 describe('NodejsFunction tests', () => {
-  beforeAll(() => {
-    mockfs({
-      'index.ts': '',
-      'package-lock.json': '',
-      '.build': {}
+  describe('with valid folder structure', () => {
+    beforeAll(() => {
+      mockfs({
+        'index.ts': '',
+        'source/index.ts': '',
+        'main.ts': '',
+        'a/b/c.ts': '',
+        'src': {
+          'index.ts': '',
+          '.build': {}
+        },
+        'package-lock.json': '',
+        '.build': {}
+      });
     });
-  });
 
-  it('Should not class constructor be thrown', async () => {
-    const stack = new Stack();
-    const factory = () => new NodejsFunction(stack, 'lambda-function', {});
-    expect(factory).not.toThrow();
-    expect(buildSync).toBeCalledTimes(1);
-    expect(stack).toHaveResource('AWS::Lambda::Function', {
-      Handler: 'index.handler',
+    beforeEach(() => {
+      (buildSync as jest.Mock).mockReset();
+    });
+
+    it.each(Runtime.ALL.filter(r => r.family !== RuntimeFamily.NODEJS))('Should be thrown due to not supported runtime', (runtime) => {
+      const constructor = () => new NodejsFunction(new Stack(), 'lambda-function', { runtime });
+      expect(constructor).toThrowError(/^Only `NODEJS` runtimes are supported.$/);
+    });
+
+    it('Should not be thrown', () => {
+      const stack = new Stack();
+      const constructor = () => new NodejsFunction(stack, 'lambda-function');
+      expect(constructor).not.toThrow();
+      expect(buildSync).toBeCalledTimes(1);
+      expect(stack).toHaveResource('AWS::Lambda::Function', {
+        Handler: 'index.handler',
+      });
+    });
+
+    it.each`
+      handler                   | entry
+      ${null}                   | ${'index.ts'}
+      ${'source/index.handler'} | ${'source/index.ts'}
+      ${'main.func'}            | ${'main.ts'}
+      ${'a/b/c.h'}              | ${'a/b/c.ts'}
+    `('Should be valid entry with default rootDir', ({ handler, entry }) => {
+      new NodejsFunction(new Stack(), 'lambda-function', { handler });
+      expect(buildSync).toHaveBeenCalledWith(expect.objectContaining({ entryPoints: [entry] }));
+    });
+
+    it('Should be valid outdir with custom rootDir', () => {
+      new NodejsFunction(new Stack(), 'lambda-function', { rootDir: path.join(__dirname, '../src') });
+      expect(buildSync).toHaveBeenCalledWith(expect.objectContaining({ outdir: path.join(__dirname, '../src', '.build') }));
+    });
+
+    afterAll(() => {
+      mockfs.restore();
     });
   });
 
-  afterAll(() => {
-    mockfs.restore();
+  describe('with invalid folder structure', () => {
+    beforeAll(() => {
+      mockfs();
+    });
+
+    it('Should be thrown due to unrecognised root directory', () => {
+      const constructor = () => new NodejsFunction(new Stack(), 'lambda-function');
+      expect(constructor).toThrowError(/^Cannot find root directory./);
+    });
+
+    afterAll(() => {
+      mockfs.restore();
+    });
   });
 });

tsconfig.json

@@ -6,6 +6,7 @@
     "declaration": true,
     "skipLibCheck": true,
     "esModuleInterop": true,
+    "strictNullChecks": true,
     "lib": ["ES2017"]
   },
   "exclude": [