Top Drupal 10 deprecations to cover

Preliminary top 13 results as of 2021 March 31 for current 5420 Drupal 9 compatible projects:

1. 6981 uses (in 444 projects) Call to deprecated method drupalPostForm() of class Drupal\Tests\BrowserTestBase. Deprecated in drupal:9.1.0 and is removed from drupal:10.0.0. Use $this->submitForm() instead.
2. 3925 uses (in 189 projects) Call to deprecated method assertText() of class Drupal\Tests\BrowserTestBase. Deprecated in drupal:8.2.0 and is removed from drupal:10.0.0. Use - $this->assertSession()->responseContains() for non-HTML responses, like XML or Json. - $this->assertSession()->pageTextContains() for HTML responses. Unlike the deprecated assertText(), the passed text should be HTML decoded, exactly as a human sees it in the browser.
3. 2142 uses (in 150 projects) Call to deprecated method assertEqual() of class Drupal\Tests\BrowserTestBase. Deprecated in drupal:8.0.0 and is removed from drupal:10.0.0. Use $this->assertEquals() instead.
4. 1421 uses (in 31 projects) Call to deprecated method assertIdentical() of class Drupal​\​Tests​\​BrowserTestBase. Deprecated in drupal:8.0.0 and is removed from drupal:10.0.0. Use $this->assertSame() instead.
5. 1183 uses (in 185 projects) Call to deprecated method assertResponse() of class Drupal\Tests\BrowserTestBase. Deprecated in drupal:8.2.0 and is removed from drupal:10.0.0. Use $this->assertSession()->statusCodeEquals() instead.
6. 1025 uses (in 84 projects) Call to deprecated method assertEqual() of class Drupal​\​KernelTests​\​KernelTestBase. Deprecated in drupal:8.0.0 and is removed from drupal:10.0.0. Use $this->assertEquals() instead.
7. 849 uses (in 107 projects) Call to deprecated method assertRaw() of class Drupal\Tests\BrowserTestBase. Deprecated in drupal:8.2.0 and is removed from drupal:10.0.0. Use $this->assertSession()->responseContains() instead.
8. 737 uses (in 77 projects) Call to deprecated method assertFieldByName() of class Drupal\Tests\BrowserTestBase. Deprecated in drupal:8.2.0 and is removed from drupal:10.0.0. Use $this->assertSession()->fieldExists() or $this->assertSession()->buttonExists() or $this->assertSession()->fieldValueEquals() instead.
9. 574 uses (in 72 projects) Call to deprecated method assertNoText() of class Drupal​\​Tests​\​BrowserTestBase. Deprecated in drupal:8.2.0 and is removed from drupal:10.0.0. Use - $this->assertSession()->responseNotContains() for non-HTML responses, like XML or Json. - $this->assertSession()->pageTextNotContains() for HTML responses. Unlike the deprecated assertNoText(), the passed text should be HTML decoded, exactly as a human sees it in the browser.
10. 413 uses (in 199 projects) Class [redacted] extends deprecated class Symfony\Component\EventDispatcher\Event: since Symfony 4.3, use "Symfony\Contracts\EventDispatcher\Event" instead
11. 364 uses (in 81 projects) Call to deprecated method setMethods() of class PHPUnit\Framework\MockObject\MockBuilder: sebastianbergmann/phpunit#3687
12. 336 uses (in 37 projects) Call to deprecated method assertFieldChecked() of class Drupal​\​Tests​\​BrowserTestBase. Deprecated in drupal:8.2.0 and is removed from drupal:10.0.0. Use $this->assertSession()->checkboxChecked() instead.
13. 244 uses (in 49 projects) Call to deprecated function drush_log().

I think 10 and 11 would be covered by other existing rectors. Not surprisingly almost all of these are about test methods that were mostly deprecated a long time ago and are already actionable to fix on Drupal 9 compatible projects within Drupal 9.

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I will be breaking these into separate issues as time allows.