title: Setting up tsconfig with spec/test folder
body: <p>Say I put my code under <code>src</code> and tests under <code>spec</code>:</p>
  
  <pre><code>+ spec
  + --- classA.spec.ts
  + src
  + --- classA.ts
  + --- classB.ts
  + --- index.ts
  + tsconfig.json
  </code></pre>
  
  <p>I want to only transpile <code>src</code> to the <code>dist</code> folder. Since <code>index.ts</code> is the entry point of my package, my <code>tsconfig.json</code> look like this:</p>
  
  <pre><code>{
    "compileOptions": {
      "module": "commonjs"
      "outDir": "dist"
    },
    "files": {
      "src/index.ts",
      "typings/main.d.ts"
    }
  }
  </code></pre>
  
  <p>However, this <code>tsconfig.json</code> does not include the test files so I could not resolve dependencies in them.</p>
  
  <p>On the other hand, if I include the test files into <code>tsconfig.json</code> then they are also transpiled to <code>dist</code> folder.</p>
  
  <p>How do I solve this problem?</p>