Migrate testing framework to jest and add more tests

[shiqimei]

I was thinking to migrate our testing framework from alsation to jest for the following considerations:

Reliability. Compared to alsation, jest is an actively developed and maintained open-source project led by facebook, which has already gained a lot of attention from the community. The former is a personal open-source project mainly maintained by @ jamesadarich, which is at risk of no longer maintaining.

Ecosystem Jest has a stronger community, which means we will benefit from abundant tools contributed by the community. For instance, vscode-jest would bring us seamless VSCode integration; babel-jest can give jest the ability to support TypeScript (now it has been merged into jest's main repository). Because of the stronger community, It's much easier for us to find solutions from the community's discussions when meeting the bugs.

Easy Migration We can do this migration without too much pain.

[codecov[bot]]

Codecov Report

Merging #180 (303ca67) into beta-external-component (a34d69c) will decrease coverage by 12.54%. The diff coverage is n/a.

@@                     Coverage Diff                      @@
##           beta-external-component     #180       +/-   ##
============================================================
- Coverage                    55.49%   42.94%   -12.55%     
============================================================
  Files                           68       66        -2     
  Lines                         2402     2191      -211     
  Branches                       360      356        -4     
============================================================
- Hits                          1333      941      -392     
- Misses                        1069     1250      +181     

Impacted Files	Coverage Δ
src/server/ProxiedApp.ts	2.89% <ø> (-11.21%)	:arrow_down:
src/server/compiler/AppCompiler.ts	19.87% <ø> (-6.17%)	:arrow_down:
src/server/compiler/AppPackageParser.ts	14.08% <ø> (-7.72%)	:arrow_down:
src/server/errors/RequiredApiVersionError.ts	0.00% <ø> (-100.00%)	:arrow_down:
src/server/logging/AppConsole.ts	100.00% <ø> (+1.96%)	:arrow_up:
src/server/misc/Utilities.ts	35.29% <ø> (-13.55%)	:arrow_down:
src/server/misc/DisabledApp.ts	0.00% <0.00%> (-100.00%)	:arrow_down:
src/server/managers/AppSlashCommandManager.ts	4.48% <0.00%> (-94.90%)	:arrow_down:
src/server/managers/AppSlashCommand.ts	32.25% <0.00%> (-64.72%)	:arrow_down:
... and 64 more

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[d-gubert]

Hey @lolimay ! Could you edit the description to add some of the reasons for the migration (e.g. benefits of Jest vs Alsatian)? Thanks :D

[shiqimei]

Hey @lolimay ! Could you edit the description to add some of the reasons for the migration (e.g. benefits of Jest vs Alsatian)? Thanks :D

Added :)