yarn test: all tests passed but returned "error Command failed with exit code 1"
<p>I used to use npm but recently switched to yarn. When I run <code>yarn test</code> it shows all tests passed but below says <code>error Command failed with exit code 1</code> with no other information on what could have caused this error</p>

<p>node version: 6.3.1</p>

<p>yarn version: 0.16.3</p>

<p>potential cause
<code>console.error node_modules/core-js/modules/es6.promise.js:117
    Unhandled promise rejection Error: Actions may not be an undefined.
        at dispatch (/node_modules/redux-mock-store/lib/index.js:35:19)
        at /node_modules/redux-thunk/lib/index.js:14:16
        at dispatch (/node_modules/redux/lib/applyMiddleware.js:45:18)
        at /src/actions/ontologies.js:159:7
        at run (/node_modules/core-js/modules/es6.promise.js:87:22)
        at /node_modules/core-js/modules/es6.promise.js:100:28
        at flush (/node_modules/core-js/modules/_microtask.js:18:9)
        at process._tickCallback (internal/process/next_tick.js:103:7)</code></p>