assertNoErrorMessage example

$this->drupalGet('error-test/generate-warnings');
    $this->assertSession()->statusCodeEquals(200);
    $this->assertErrorMessage($error_notice);
    $this->assertErrorMessage($error_warning);
    $this->assertErrorMessage($error_user_notice);
    $this->assertSession()->responseNotContains('<pre class="backtrace">');

    // Set error reporting to not collect notices.     $config->set('error_level', ERROR_REPORTING_DISPLAY_SOME)->save();
    $this->drupalGet('error-test/generate-warnings');
    $this->assertSession()->statusCodeEquals(200);
    $this->assertNoErrorMessage($error_notice);
    $this->assertErrorMessage($error_warning);
    $this->assertErrorMessage($error_user_notice);
    $this->assertSession()->responseNotContains('<pre class="backtrace">');

    // Set error reporting to not show any errors.     $config->set('error_level', ERROR_REPORTING_HIDE)->save();
    $this->drupalGet('error-test/generate-warnings');
    $this->assertSession()->statusCodeEquals(200);
    $this->assertNoErrorMessage($error_notice);
    $this->assertNoErrorMessage($error_warning);
    $this->assertNoErrorMessage($error_user_notice);