✅ Introduce a new way to mock values in unit tests

[BenoitZugmeyer]

Motivation

This is a proposal to allow mocking values (mostly functions) within tests.

The current way to mock values used within a function is to pass them as argument of that function. For example:

// foo.ts
import { startBar } from 'bar'

function createFoo(startBarImpl = startBar) {
  const bar = startBarImpl()
}


// foo.spec.ts
it('create foo', () => {
  createFoo(mockStartBar)
})

However, forces to have unecessary extra arguments in functions. Impls also need to be propagated within subfunctions:

// foo.ts
function createFoo(startBarImpl = startBar) {
  const baz = trackBaz(startBarImpl)
}

// baz.ts
function trackBaz(startBarImpl = startBar) {
}

This PR introduce a new way to mock values that is similar to a lightweight dependency injection system. Values that can be mocked should be wrapped in a mocked() call when used, and tests can use mockValue() to replace the value or mockWithSpy() to replace it with a jasmine spy. The example above would be implemented as:

// foo.ts
import { startBar } from 'bar'

function createFoo() {
  const bar = mockable(startBar)()
}

// foo.spec.ts
it('create foo', () => {
  replaceMockable(startBar, mockStartBar)
  // or
  replaceMockableWithSpy(startBar).and.callFake(mockStartBar)
  createFoo()
})

Changes

The first 2 commits does a bit of spec cleaning.

Then, we introduce mockable capabilities and use it in tests, mostly to replace all *Impl arguments and location mocking.

Please review commit by commit.

Test instructions

If tests passes, it should be good.

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[datadog-datadog-prod-us1]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 90.91%
• Overall Coverage: 77.27% (+0.01%)

View detailed report

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[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	169.44 KiB	169.55 KiB	+107 B	+0.06%	✅
Rum Profiler	4.31 KiB	4.31 KiB	0 B	0.00%	✅
Rum Recorder	24.54 KiB	24.54 KiB	0 B	0.00%	✅
Logs	56.72 KiB	56.62 KiB	-104 B	-0.18%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	126.26 KiB	126.18 KiB	-84 B	-0.06%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.004	0.0062	+55.00%
RUM - add action	0.0124	0.0194	+56.45%
RUM - add error	0.0121	0.0163	+34.71%
RUM - add timing	0.0025	0.0034	+36.00%
RUM - start view	0.0118	0.0217	+83.90%
RUM - start/stop session replay recording	0.0007	0.001	+42.86%
Logs - log message	0.0149	0.0192	+28.86%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	27.32 KiB	27.49 KiB	+172 B
RUM - add action	50.83 KiB	50.02 KiB	-832 B
RUM - add timing	26.93 KiB	26.14 KiB	-810 B
RUM - add error	57.36 KiB	55.71 KiB	-1.65 KiB
RUM - start/stop session replay recording	26.81 KiB	25.92 KiB	-910 B
RUM - start view	452.06 KiB	454.59 KiB	+2.52 KiB
Logs - log message	45.88 KiB	46.69 KiB	+829 B

🔗 RealWorld