diff --git a/.travis.yml b/.travis.yml
index 6983d72..ff544ca 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,12 +1,24 @@
 language: php
 
 php:
-  - 5.3
+# - 5.3 # requires old distro
   - 5.4
   - 5.5
   - 5.6
-  - 7
-  - hhvm
+  - 7.0
+  - 7.1
+  - 7.2
+  - hhvm # ignore errors, see below
+
+# lock distro so new future defaults will not break the build
+dist: trusty
+
+matrix:
+  include:
+    - php: 5.3
+      dist: precise
+  allow_failures:
+    - php: hhvm
 
 sudo: false
 
diff --git a/README.md b/README.md
index 28a773c..087e7b3 100644
--- a/README.md
+++ b/README.md
@@ -200,7 +200,8 @@ See also the [CHANGELOG](CHANGELOG.md) for details about version upgrades.
 
 ## Tests
 
-To run the test suite, you first need to clone this repo and then install all dependencies [through Composer](http://getcomposer.org):
+To run the test suite, you first need to clone this repo and then install all
+dependencies [through Composer](http://getcomposer.org):
 
 ```bash
 $ composer install
diff --git a/composer.json b/composer.json
index c38c393..c7028c1 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,7 @@
     },
     "require-dev": {
         "react/event-loop": " ^0.4 || ^0.3",
-        "phpunit/phpunit": "^5.0 || ^4.8",
+        "phpunit/phpunit": "^6.0 || ^5.7 || ^4.8.35",
         "react/stream": "^1.0 || ^0.7 || ^0.6"
     }
 }
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 91ad7d3..4ff6600 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -1,10 +1,12 @@
 <?php
 
+use PHPUnit\Framework\TestCase as BaseTestCase;
+
 require_once __DIR__ . '/../vendor/autoload.php';
 
 error_reporting(-1);
 
-class TestCase extends PHPUnit_Framework_TestCase
+class TestCase extends BaseTestCase
 {
     protected function expectCallableNever()
     {
@@ -32,35 +34,13 @@ protected function expectCallableOnceWith($value)
         $mock
             ->expects($this->once())
             ->method('__invoke')
-            ->with($this->equalTo($value));
-
-        return $mock;
-    }
-
-    protected function expectCallableOnceParameter($type)
-    {
-        $mock = $this->createCallableMock();
-        $mock
-            ->expects($this->once())
-            ->method('__invoke')
-            ->with($this->isInstanceOf($type));
+            ->with($value);
 
         return $mock;
     }
 
-    /**
-     * @link https://github.com/reactphp/react/blob/master/tests/React/Tests/Socket/TestCase.php (taken from reactphp/react)
-     */
     protected function createCallableMock()
     {
-        return $this->getMockBuilder('CallableStub')->getMock();
-    }
-}
-
-class CallableStub
-{
-    public function __invoke()
-    {
+        return $this->getMockBuilder('stdClass')->setMethods(array('__invoke'))->getMock();
     }
 }
-