fix: Handle the case when staged-git-files errors properly (#267)

Closes #264

test/runAll.spec.js

@@ -1,15 +1,25 @@
 /* eslint no-console: 0 */
 
+import sgfMock from 'staged-git-files'
 import { getConfig } from '../src/getConfig'
 import runAll from '../src/runAll'
 
+jest.mock('staged-git-files')
+
+sgfMock.mockImplementation((params, callback) => {
+  callback(null, [])
+})
+
 const packageJson = {
   scripts: {
     mytask: 'echo "Running task"'
   }
 }
 
 describe('runAll', () => {
+  afterEach(() => {
+    sgfMock.mockClear()
+  })
   it('should throw when invalid config is provided', () => {
     expect(() => runAll(packageJson, {})).toThrowErrorMatchingSnapshot()
     expect(() => runAll(packageJson)).toThrowErrorMatchingSnapshot()
@@ -30,4 +40,12 @@ describe('runAll', () => {
     expect.assertions(1)
     return expect(runAll(packageJson, getConfig({}))).resolves.toEqual('No tasks to run.')
   })
+
+  it('should reject the promise when staged-git-files errors', () => {
+    sgfMock.mockImplementation((params, callback) => {
+      callback('test', undefined)
+    })
+    expect.assertions(1)
+    return expect(runAll(packageJson, getConfig({}))).rejects.toEqual('test')
+  })
 })