Extend Jest Tests

[acrosman]

Summary
With the merge of #49 which closed #48, we now have some test coverage. Bu there is only a little test coverage at the moment. Over time we'll work toward more.

This issue is for generally reminding of the need to include more tests. Additional sub-issues and related issues will be added for specific requests. If you'd like to add tests generically, you may want to look at the functions in src/sf_calls.js and src/preferences.js that do not callback to the main window directly (the project already includes rewire to make it easy to access non-exported features of the modules).

There are also no tests currently covering the render JS files, which are fairly extensive as well.

Specific Testing Issues

• Add/Find Mock library for Knex, and add tests to cover functions that call the database. #64
• Add/Find Mock library for Electron.js, and add tests to cover IPC calls. #65
• Add/Find Mock library for Electron.js, and add tests to cover dialogs interactions. #66
• Extend test of buildSchema() in src/sf_calls.js to cover more details and field examples. #67
• Add direct test of buildFields() in src/sf_calls.js to allow simple review of more examples. #68
• Start tests of preferences.js to cover basic module structure. #69
• Create tests for apps/render.js to cover helper functions. #70

[imrishabh18]

I have started to learn jest and wanted to contribute to some open source projects. What do you think would be best to start with here @acrosman ?

[acrosman]

Any one of:

• Extend test of buildSchema() in src/sf_calls.js to cover more details and field examples. #67
• Add direct test of buildFields() in src/sf_calls.js to allow simple review of more examples. #68
• Start tests of preferences.js to cover basic module structure. #69

All three have a pattern to review from other tests so you aren't starting totally from scratch. The last one is a bit more of a free space to run since it involves starting a whole new test file and the least figuring out how existing code works. The first two have clearer patterns to follow, but also require reading and understanding the code you're testing more deeply.