assertFieldInRegion example

$this->assertSession()->elementTextContains('css', '.layout__region--content', 'The field test text value');
    $this->drupalGet('entity_test/1');
    $this->assertSession()->elementNotExists('css', '.layout__region--content');
  }

  /** * Tests the use of field layout for entity form displays. */
  public function testEntityForm() {
    // By default, the one-column layout is used.     $this->drupalGet('entity_test/manage/1/edit');
    $this->assertFieldInRegion('field_test_text[0][value]', 'content');

    // The one-column layout is in use.     $this->drupalGet('entity_test/structure/entity_test/form-display');
    $this->assertEquals(['Content', 'Disabled'], $this->getRegionTitles());

    // Switch the layout to two columns.     $this->click('#edit-field-layouts');
    $this->getSession()->getPage()->selectFieldOption('field_layout', 'layout_twocol');
    $this->assertSession()->assertWaitOnAjaxRequest();
    $this->submitForm([], 'Save');