fix(expect): always show custom message

[eryue0220]

This pr is to solve #6206

[codecov]

Codecov Report

Attention: Patch coverage is 92.07921% with 24 lines in your changes missing coverage. Please review.

Project coverage is 96.32%. Comparing base (cc9a7c0) to head (1e6c9d8).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
expect/_matchers.ts	91.11%	23 Missing ⚠️
expect/_assert_not_equals.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6217      +/-   ##
==========================================
- Coverage   96.49%   96.32%   -0.17%     
==========================================
  Files         536      543       +7     
  Lines       41179    41598     +419     
  Branches     6175     6314     +139     
==========================================
+ Hits        39735    40071     +336     
- Misses       1401     1485      +84     
+ Partials       43       42       -1     

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[kt3k]

I think this part should be something like:

const defaultMessage = `Expected the value not to be close to ${expected} (using ${numDigits} digits), but it is`
throw new AssertionError(
  context.customMessage ? `${context.customMessage}: ${defaultMessage}` : defaultMessage
);

Vitest, for example, shows the custom message like the above.

In Vitest:

expect(42, "custom message").toEqual(43);

This assertion error shows the message like:

AssertionError: custom message: expected 42 to deeply equal 43

- Expected
+ Received

- 43
+ 42

[eryue0220]

Updated

[kt3k]

Oh, I missed this message. Sorry for the delay!

[kt3k]

I vendored assertIsError to expect/ because the suggested change was not desired for @std/assert/is-error.

[kt3k]

LGTM. Thanks!