WIP - Run all tests using Jest

[lindapaiste]

Completed:

Settings:

• Add "_test\\.js" alongside the deafult Jest testRegex to match all index_test.js files.
• Add testEnvironmentOptions: { resources: "usable" } to Jest config so that images will call the onload function.
• Set env: { jest: true } in .eslint.js to fix es-lint errors re: undefined variable jest.
• Install node polyfill for canvas.

Rewrites:

• Import the functions to test from local files instead of a global ml5 variable.
  • Rewrite test imports from const { charRNN } = ml5; to import charRNN from './index';.
  • import tf directly from @tensorflow/tfjs in NeuralNetwork instead of using ml5.tf alias.
• Replace all instances of jasmine.DEFAULT_TIMEOUT_INTERVAL = n; with jest.setTimeout(n);.
• Replace spyOn with jest.spyOn (which internally calls the jasmine spyOn function).
  • Modify chained function calls, eg. .and.callFake to .mockImplementation, .and.returnValue to .mockReturnValue, etc.

General Clean-up:

• Move common logic re: image creation into testUtils.

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TODO:

• Prevent errors from empty test files.
  • I put an empty describe in each file and added passWithNoTests: true to Jest config, but this doesn't work.
• Fix fetch calls which are executed internally in the face-api.js package.
  • Adding "cross-fetch/polyfill" to setupFiles in Jest config prevents the fetch errors, but then the test just hangs.
• Guard references to ImageData to avoid error ImageData is not defined in the node environment and/or install polyfill.
• Use @tensorflow/tfjs-node in tests.