JS: show test changes after #15823

[RasmusWL]

This PR is a journey for me into better understanding the JS CodeQL analysis, by trying to write tests to show the effect of #15823. I've written some tests that initially fail on commit 245cd5c (parent of PR merge commit), and then tested them again on 7c35309 (PR merge commit)

I was able to highlight the effect of the Detect more FunctionStyleClasses commit, see the change in javascript/ql/test/ApiGraphs/classes/VerifyAssertions.expected.

I had expected that the step defined here

codeql/javascript/ql/lib/semmle/javascript/dataflow/internal/StepSummary.qll

Lines 120 to 121 in 13e3a51

	CallGraph::impliedReceiverStep(pred, succ) and
	summary = CallStep()

would cause at least the obj_ type-tracking test to pass after the changes in the PR, but that was not the case.

So I wasn't able to write a test that highlights the impact of the change in f5d014b, even though I can see the change in impliedReceiverStep when quick-eval'ing locally. @asgerf can you highlight the end-result impact of that commit? 😕

[asgerf]

Try putting import 'dummy'; at the top so the file is seen as a module. Otherwise all variables at the top-level become global variables which are tracked less precisely.

[RasmusWL]

That changed initial test results (in positive way), but I still don't see impact of implicit receiver step in the test changes after merging in the PR: ac05c80

[asgerf]

Previously there was a requirement that the host object was an object literal or function. That restriction was lifted in the PR, but in these test, it seems the host object is always an object literal, so they are not affected by the change.

[RasmusWL]

After some more back and forth locally, we finally managed to make a nice test example of the implicit receiver step 👍