Unit test 100% coverage

[gabrielegranello]

What does this PR do?

It expands the suite of unit tests following #71

How?

By checking which lines of code were not read in the jest report, I have added a few extra tests to explore those lines. In doing so, I caught a small bug in the Mortgage.ts class.
Furthermore, the jest.config.ts file is modified to force 100% of the code coverage while testing.

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Name	Status	Preview	Comments	Updated (UTC)
fairhold-dashboard	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 28, 2024 8:49am

[gabrielegranello]

This is interesting... When testing on my machine I get to 100%, but when testing on Github the percentage is lower. How can this be possible?

[gabrielegranello]

That drove me bananas I swear. Basically the node version on my local machine was 18.17.0; In the GitHub Actions, node version was 18. That meant for some obscure reason unknown to me that the line coverage was different. I have even made sure to delete the cache when running the test. I still can't explain myself why but now it works

[DafyddLlyr]

Amazing, good result here! Great to see that we caught some issues this way as well.

Not exactly sure of the reason you were having issues with Node and coverage percentages. One good idea would be to set up a .nvmrc file in the root of the project which may allow us to ensure we have a standard version of Node locally when running the app? https://dev.to/kibumpng/consistency-and-efficiency-with-nvmrc-30mi

[DafyddLlyr]

Magic number! 🪄 🎩 🐇

Maybe if (!isFinalYear) would be a suitable variable name we could use?

const isFinalYear = i == this.termYears - 2

Also, often positive conditions are easier to read - could we use if (isFinalYear) as a guard clause and un-nest this condition?

[gabrielegranello]

Thanks Daf, it makes a lot of sense. Were you thinking of something like this?

    const finalYear = this.termYears - 2;
    for (let i = 0; i < this.termYears - 1; i++) {
      if (i == finalYear) {
        yearlyPayment = remainingBalance;
      } else {
        yearlyPayment = this.monthlyPayment * MONTHS_PER_YEAR;
      }

[DafyddLlyr]

Here's a version using a guard clause pattern -

const isFinalYear = this.termYears - 2;
for (let i = 0; i < this.termYears - 1; i++) {
  if (i == isFinalYear) {
    yearlyPayment = remainingBalance;
    continue;
  }
  
  yearlyPayment = this.monthlyPayment * MONTHS_PER_YEAR;
}

Docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/continue

[DafyddLlyr]

P.S. GitHub (and lots of other markdown / code tools - even Notion) allow you to annotate code blocks with a language to get the nice syntax highlighting features 💅

Docs: https://docs.github.com/en/get-started/writing-on-github/working-with-advanced-formatting/creating-and-highlighting-code-blocks#syntax-highlighting

[gabrielegranello]

Thanks for taking the time to spell it out @DafyddLlyr, really appreciated.
It was the first time I have come across this patter for loops, I have always used if/else. I can see why this structure is better. Also great tip for Typescript!

[DafyddLlyr]

🙌