…las-grekas)This PR was merged into the 2.7 branch.Discussion----------[Form] Fix missing choices_as_values=true in tests| Q             | A| ------------- | ---| Bug fix?      | no| New feature?  | no| BC breaks?    | no| Deprecations? | no| Tests pass?   | yes| Fixed tickets | -| License       | MIT| Doc PR        | -Commits-------2a16e87 [Form] Fix missing choices_as_values=true in tests

…ion on-demand (nicolas-grekas)This PR was merged into the 2.8 branch.Discussion----------[Bridge\PhpUnit] Display the stack trace of a deprecation on-demand| Q             | A| ------------- | ---| Bug fix?      | no| New feature?  | yes| BC breaks?    | no| Deprecations? | no| Tests pass?   | yes| Fixed tickets | -| License       | MIT| Doc PR        | -This PR has been essential into making#16708, and I think everyone working on a 3.0 migration will need this.Example:```$ SYMFONY_DEPRECATIONS_HELPER=/FormExtensionBootstrap3LayoutTest/ ./phpunit src/Symfony/Bridge/Twig/PHPUnit 4.8.18 by Sebastian Bergmann and contributors.Testing src/Symfony/Bridge/Twig/................................................Remaining deprecation triggered by Symfony\Bridge\Twig\Tests\Extension\FormExtensionBootstrap3LayoutTest::testSingleChoiceGrouped:The value "false" for the "choices_as_values" option is deprecated since version 2.8 and will not be supported anymore in 3.0. Set this option to "true" and flip the contents of the "choices" option instead.Stack trace:#0 src/Symfony/Component/Form/Extension/Core/Type/ChoiceType.php(286): trigger_error()#1 src/Symfony/Component/OptionsResolver/OptionsResolver.php(962): Symfony\Component\Form\Extension\Core\Type\ChoiceType->Symfony\Component\Form\Extension\Core\Type\{closure}()#2 src/Symfony/Component/Form/Extension/Core/Type/ChoiceType.php(277): Symfony\Component\OptionsResolver\OptionsResolver->offsetGet()#3 src/Symfony/Component/OptionsResolver/OptionsResolver.php(962): Symfony\Component\Form\Extension\Core\Type\ChoiceType->Symfony\Component\Form\Extension\Core\Type\{closure}()#4 src/Symfony/Component/OptionsResolver/OptionsResolver.php(791): Symfony\Component\OptionsResolver\OptionsResolver->offsetGet()#5 src/Symfony/Component/Form/ResolvedFormType.php(156): Symfony\Component\OptionsResolver\OptionsResolver->resolve()#6 src/Symfony/Component/Form/FormFactory.php(119): Symfony\Component\Form\ResolvedFormType->createBuilder()#7 src/Symfony/Component/Form/FormFactory.php(48): Symfony\Component\Form\FormFactory->createNamedBuilder()#8 src/Symfony/Component/Form/Tests/AbstractBootstrap3LayoutTest.php(540): Symfony\Component\Form\FormFactory->createNamed()#9 [internal function]: Symfony\Component\Form\Tests\AbstractBootstrap3LayoutTest->testSingleChoiceGrouped()#10 {main}KO src/Symfony/Bridge/Twig/```Commits-------5a88fb6 [Bridge\PhpUnit] Display the stack trace of a deprecation on-demand