test it ends process on failure to read

tests/read_previous_event.test.js

@@ -0,0 +1,72 @@
+import { read_previous_events } from '../src/logic';
+
+beforeEach(jest.restoreAllMocks);
+
+const fs = require('fs').promises;
+const filesystem = require('fs');
+const process = require('process');
+
+describe('read_previous_event', () => {
+  [null, undefined].forEach((path) =>
+    it(`it should return an empty array if path is ${path}`, () => {
+      expect.assertions(1);
+      read_previous_events(path).then((res) => expect(res).toEqual([]));
+    }),
+  );
+
+  it(`it should return an empty array if path does not exist`, () => {
+    const exist = jest
+      .spyOn(filesystem, 'existsSync')
+      .mockImplementation(() => false);
+    expect.assertions(3);
+    return read_previous_events().then((res) => {
+      expect(res).toEqual([]);
+      expect(exist).toHaveBeenCalledTimes(1);
+      expect(exist).toHaveBeenCalledWith(undefined);
+    });
+  });
+
+  it(`it should return an empty array if parse says so`, () => {
+    jest.spyOn(filesystem, 'existsSync').mockImplementation(() => true);
+    const mock = jest
+      .spyOn(fs, 'readFile')
+      .mockImplementation(() => Promise.resolve('[]'));
+    expect.assertions(3);
+    const path = 'directory';
+    return read_previous_events(path).then((res) => {
+      expect(mock).toHaveBeenCalledTimes(1);
+      expect(mock).toHaveBeenCalledWith(path, { encoding: 'utf-8' });
+      expect(res).toEqual([]);
+    });
+  });
+
+  it(`it should end process if file cannot be read`, () => {
+    jest.spyOn(filesystem, 'existsSync').mockImplementation(() => true);
+    const exit = jest.spyOn(process, 'exit').mockImplementation(() => true);
+    const error = jest.spyOn(console, 'error').mockImplementation(() => true);
+    const mock = jest
+      .spyOn(fs, 'readFile')
+      .mockImplementation(() => Promise.reject('ERROR'));
+    expect.assertions(2);
+    const path = 'directory';
+    return read_previous_events(path).then((res) => {
+      expect(exit).toHaveBeenCalledWith(1);
+      expect(error).toHaveBeenCalledWith('ERROR');
+    });
+  });
+
+  it(`it should end process if JSON cannot be parsed`, () => {
+    jest.spyOn(filesystem, 'existsSync').mockImplementation(() => true);
+    const exit = jest.spyOn(process, 'exit').mockImplementation(() => true);
+    const error = jest.spyOn(console, 'error').mockImplementation(() => true);
+    const mock = jest
+      .spyOn(fs, 'readFile')
+      .mockImplementation(() => Promise.resolve('ERROR'));
+    expect.assertions(2);
+    const path = 'directory';
+    return read_previous_events(path).then((res) => {
+      expect(exit).toHaveBeenCalledWith(1);
+      expect(error).toHaveBeenCalledTimes(1);
+    });
+  });
+});