test: improve test coverage

[sun0day]

Description

All PRs from this branch intend to increase UT coverage and optimize vueuse source code. I will continuously commit test code to this branch.

All commits in this branch are atomic, feel free to merge PR at any time.@antfu

History PRs:

• test: impove test coverage #2185
• test: improve test coverage #2233
• test: improve test coverage #2256
• test: improve test coverage #2300

Updated UT Coverage

api	statements	branches	functions	lines
createEventHook	100% ⬆️	100%	100% ⬆️	100% ⬆️
useTimestamp	100% ⬆️	100% ⬆️	100% ⬆️	100% ⬆️
useNow	100% ⬆️	100% ⬆️	100% ⬆️	100% ⬆️
useEventListener	100% ⬆️	100% ⬆️	100%	100% ⬆️
watchThrottled	100% ⬆️	100%	100% ⬆️	100% ⬆️
watchDebounced	100% ⬆️	100%	100% ⬆️	100% ⬆️

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Test

Before submitting the PR, please make sure you do the following

• Read the Contributing Guidelines.
• Read the Pull Request Guidelines.
• Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
• Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. fixes #123).
• Ideally, include relevant tests that fail without this PR but pass with it.

[sun0day]

Build CI failed twice when fetching contributors in node16.x 😭 @sxzz @antfu

[sxzz]

@sun0day I just triggered to re-run it. It works now. 😄

[sun0day]

@sun0day I just triggered to re-run it. It works now. 😄

ok

[younggglcy]

@sun0day Hello, I've found that the tests of watchDebounced have a certain probability of failure in the vue2 environment. This is mainly due to these lines. CI workflows of #2376 and #2386 can be used as reference for your needs.

Can u take some spare time to look at it please? And finally appreciate for your great work and the effort you put!