diff --git a/.travis.yml b/.travis.yml
index 8c24c0cf..bf2f057e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -6,16 +6,10 @@ cache:
     directories:
         - $HOME/.composer/cache/files
 
-php:
-    - 5.5
-    - 5.6
-    - 7.0
-    - 7.1
-    - 7.2
-
 env:
     global:
         - TEST_COMMAND="composer test"
+        - SYMFONY_PHPUNIT_VERSION="6.3"
 
 branches:
     except:
@@ -24,26 +18,48 @@ branches:
 matrix:
     fast_finish: true
     include:
+          # Minimum supported Symfony version and latest PHP version
+        - php: 7.1
+          env: DEPENDENCIES="minimum" COVERAGE=true TEST_COMMAND="composer test-ci" SYMFONY_DEPRECATIONS_HELPER="weak" SYMFONY_PHPUNIT_VERSION="5.7"
+
+          # Test the latest stable release
         - php: 5.5
-          env: COMPOSER_FLAGS="--prefer-stable --prefer-lowest" COVERAGE=true TEST_COMMAND="composer test-ci"
-        - php: 7.2
-          env: DEPENDENCIES=dev
-        - php: hhvm
-          dist: trusty
-          # Test against LTS versions
+          env: SYMFONY_PHPUNIT_VERSION="5.7"
+        - php: 5.6
+          env: SYMFONY_PHPUNIT_VERSION="5.7"
         - php: 7.0
-          env: SYMFONY_VERSION=2.8.*
+        - php: 7.1
+        - php: 7.2
+
+          # Test LTS versions
+        - php: 5.5
+          env: DEPENDENCIES="symfony/lts:^2"
+        - php: 5.5
+          env: DEPENDENCIES="symfony/lts:^3"
+
+          # Latest commit to master
+        - php: 7.1
+          env: DEPENDENCIES="dev"
+
+    allow_failures:
+          # dev-master is allowed to fail.
+        - php: 7.1
+          env: DEPENDENCIES="dev"
 
 before_install:
-    - if [ "$SYMFONY_VERSION" != "" ]; then composer require "symfony/symfony:${SYMFONY_VERSION}" --no-update; fi;
-    - if [ "$DEPENDENCIES" = "dev" ]; then sed -i '/prefer-stable/d' composer.json; fi;
-    - if [ "$DEPENDENCIES" = "dev" ]; then perl -pi -e 's/^}$/,"minimum-stability":"dev"}/' composer.json; fi;
-    - if [ $COVERAGE != true ]; then phpenv config-rm xdebug.ini; fi;
+    - if [[ $COVERAGE != true ]]; then phpenv config-rm xdebug.ini || true; fi
+    - if [ "$DEPENDENCIES" = "minimum" ]; then COMPOSER_FLAGS="--prefer-stable --prefer-lowest"; fi;
+    - if [ "$DEPENDENCIES" = "dev" ]; then composer config minimum-stability dev; fi;
+    - if [[ $DEPENDENCIES == *"/"* ]]; then composer require --no-update $DEPENDENCIES; fi;
 
 install:
-    - travis_retry composer update ${COMPOSER_FLAGS} --prefer-dist --no-interaction
+    # To be removed when this issue will be resolved: https://github.com/composer/composer/issues/5355
+    - if [[ "$COMPOSER_FLAGS" == *"--prefer-lowest"* ]]; then composer update --prefer-dist --no-interaction --prefer-stable --quiet; fi
+    - composer update ${COMPOSER_FLAGS} --prefer-dist --no-interaction
+    - vendor/bin/simple-phpunit install
 
 script:
+    - composer validate --strict --no-check-lock
     - $TEST_COMMAND
 
 after_success:
diff --git a/Tests/Unit/Collector/StackPluginTest.php b/Tests/Unit/Collector/StackPluginTest.php
index fd56b8f1..c7416008 100644
--- a/Tests/Unit/Collector/StackPluginTest.php
+++ b/Tests/Unit/Collector/StackPluginTest.php
@@ -11,7 +11,6 @@
 use Http\HttplugBundle\Collector\StackPlugin;
 use Http\Promise\FulfilledPromise;
 use Http\Promise\RejectedPromise;
-use PHPUnit\Framework\Error\Warning;
 use PHPUnit\Framework\TestCase;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
@@ -188,8 +187,17 @@ public function testOnError()
             $this->markTestSkipped();
         }
 
-        //PHPUnit wrap any \Error into a \PHPUnit\Framework\Error\Warning.
-        $this->expectException(Warning::class);
+        /*
+         * Use the correct PHPUnit version
+         * PHPUnit wrap any \Error into a \PHPUnit\Framework\Error\Warning.
+         */
+        if (class_exists('PHPUnit_Framework_Error')) {
+            // PHPUnit 5.7
+            $this->setExpectedException(\PHPUnit_Framework_Error::class);
+        } else {
+            // PHPUnit 6.0 and above
+            $this->expectException(\PHPUnit\Framework\Error\Warning::class);
+        }
 
         $this->collector
             ->expects($this->once())
diff --git a/composer.json b/composer.json
index ad0fe1be..887d7365 100644
--- a/composer.json
+++ b/composer.json
@@ -33,7 +33,6 @@
         "symfony/dependency-injection": "^2.8.3 || ^3.0.3"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8.35 || ^5.7 || ^6.1",
         "phpunit/php-token-stream": "^1.1.8",
         "php-http/curl-client": "^1.0",
         "php-http/socket-client": "^1.0",
@@ -41,7 +40,7 @@
         "php-http/react-adapter": "^0.2.1",
         "php-http/buzz-adapter": "^0.3",
         "php-http/mock-client": "^1.0",
-        "symfony/phpunit-bridge": "^3.2",
+        "symfony/phpunit-bridge": "^3.3 || ^4.0",
         "symfony/twig-bundle": "^2.8 || ^3.0",
         "symfony/twig-bridge": "^2.8 || ^3.0",
         "symfony/web-profiler-bundle": "^2.8 || ^3.0",
@@ -50,7 +49,7 @@
         "symfony/browser-kit": "^2.8 || ^3.0",
         "symfony/dom-crawler": "^2.8 || ^3.0",
         "polishsymfonycommunity/symfony-mocker-container": "^1.0",
-        "matthiasnoback/symfony-dependency-injection-test": "^1.0 || ^2.0",
+        "matthiasnoback/symfony-dependency-injection-test": "^1.1 || ^2.0",
         "nyholm/nsa": "^1.1"
     },
     "conflict": {
@@ -69,8 +68,8 @@
         ]
     },
     "scripts": {
-        "test": "vendor/bin/phpunit",
-        "test-ci": "vendor/bin/phpunit --coverage-text --coverage-clover=build/coverage.xml"
+        "test": "vendor/bin/simple-phpunit",
+        "test-ci": "vendor/bin/simple-phpunit --coverage-text --coverage-clover=build/coverage.xml"
     },
     "extra": {
         "branch-alias": {