chore(tests): fix and improve tests to cover latest changes

create test for success reading the files.
create test for failure when file couldn't be found.

Author: zebateira

__mocks__/webpack.js

@@ -0,0 +1 @@
+module.exports = {}

__tests__/fixtures/intl/es.json

@@ -0,0 +1,3 @@
+{
+    "spanish": "Spanish version"
+}

__tests__/gatsby-node.js

@@ -1,3 +1,5 @@
+const fs = require(`fs`)
+
 const { onCreatePage } = require(`../src/gatsby-node`)
 
 const actions = {
@@ -9,10 +11,54 @@ const mocks = {
   actions,
   page: {
     path: "/",
+    context: {},
   },
 }
 
-it(`does not crash when no pluginConfig is provided`, () => {
+beforeAll(() => {
+  // Create file src/en.json because the default option for reading a file is `./en.json`
+  fs.writeFileSync(
+    `${__dirname}/../src/en.json`,
+    JSON.stringify({ english: `English version` })
+  )
+})
+
+afterAll(() => {
+  fs.unlinkSync(`${__dirname}/../src/en.json`)
+})
+
+it(`should not crash when no pluginConfig is provided`, async () => {
   const pluginOptions = {}
-  onCreatePage(mocks, pluginOptions)
+
+  await onCreatePage(mocks, pluginOptions)
+})
+
+it(`should read translations from file and create corresponding pages`, async () => {
+  const pluginOptions = {
+    languages: [`es`],
+    defaultLanguage: `es`,
+    path: `${__dirname}/fixtures/intl`,
+  }
+
+  await onCreatePage(mocks, pluginOptions)
+
+  expect(actions.createPage.mock.calls.length).toBe(4)
+
+  // assert the pages created match the requested languages
+  expect(actions.createPage.mock.calls[0][0].path).toBe(`/`)
+  expect(actions.createPage.mock.calls[1][0].path).toBe(`/en/`)
+  expect(actions.createPage.mock.calls[2][0].path).toBe(`/`)
+  expect(actions.createPage.mock.calls[3][0].path).toBe(`/es/`)
+})
+
+it(`should crash when translations file doesn't exist`, async () => {
+  const pluginOptions = {
+    languages: [`es`, `en`],
+    defaultLanguage: `es`,
+    path: `${__dirname}/fixtures/intl`,
+  }
+
+  await expect(onCreatePage(mocks, pluginOptions)).rejects.toThrow(
+    `Cannot find module`
+  )
 })