[meta] Replace assertions with more appropriate ones

There's a bunch of calls like

 $this->assertTrue(strpos(strtolower(Html::decodeEntities($haystack)), $needle) === FALSE, $message, $group);

$this->assertNotIdentical(FALSE, strpos($query, $expected), 'The flattened query contains the comment string.');

 $this->assertNotIdentical(strpos($rendered_js, $expected_1), FALSE, 'Rendered external JavaScript with correct defer and random attributes.');

These are hardly readable with all the double negations etc etc.

Now we can use

assertStringContainsString

or

assertStringNotContainsString

and the assertStringContainsStringIgnoringCase companions and get rid of this mindblowing madness

EDIT: regex

/assert.*\(.*strpos/

Filed #3128746: Replace assertions involving calls to strpos() with more accurate string assertions

#3113077: Replace assertContains() on strings with assertStringContainsString() or assertStringContainsStringIgnoringCase() already has a parent, so I marked it related to this, not a child.

Other interesting regexes for potential issues:

=.*this->assert(?!Session)(Equal|True|NotRe|Resp): assignment of return values of assertions (possible in Simpletest, do not make sense in PHPUnit and likely signal conditional code)

>assert.*\(.*is_.*\(: possibly replaced by assertNull, assertIsObject, assertIsString, etc.

>assert(?:True|False)\(.*(?:==|===): possibly replaced by assertEquals, assertSame

#3128814: Replace assert* involving count() and an equality operator with assertCount() is pending D8 backport/commit. Moved.

Based on a lengthy Slack thread this morning, I just opened #3131946: [policy] Remove PHPUnit assertion messages when possible, and standardize remaining messages as a related (though independent) effort. Please discuss there. Thanks!

Refresshing th IS.

#3131088: Replace assertions involving calls to file_exists with assertFileExists()/assertFileNotExists() or assertDirectoryExists()/assertDirectoryNotExists() introduced some bad code in 8.9.x; I opened #3133103: [8.9 only] InstallerCustomConfigDirectoryCreateTest has bad assertions to fix this.

Proposed two new issues:

#3133288: [meta] Add custom PHPUnit assertions for common tests
#3133291: Add XPath existence assertions

What I am missing here is a guide for which kind of assertion to use. When I now write a test it is to me very confusing which kind of assertion is should use.

@daffie re #64, I find PHPUnit's list https://phpunit.readthedocs.io/en/8.5/assertions.html the best starting point to understand what default PHPUnit provides. Using those when possible it's the right choice IMHO.

Updated IS for #66

More IS updates

#77 is great, I think the link to the kanban deserves better visibility, done here.

Time to call this done? If there are other optimizations possible, phpstan-phpunit will probably spot them and we will open individual issues.

Yes, I agree.

Thanks for keeping this on track and to everyone who worked on the child issues!

This is tagged for documentation, #64. Using the advice in #66, I added a link to the list of assertions to PHPUnit in Drupal, which was the suggested place in #65 point 2.