PHPUnit 9 support (#11)

Author: remorhaz

.gitignore

@@ -3,3 +3,4 @@ build
 composer.lock
 phpunit.xml
 vendor
+.phpunit.result.cache

composer.json

@@ -18,7 +18,7 @@
         "irc": "irc://irc.freenode.org/amphp"
     },
     "require": {
-        "phpunit/phpunit": "^6 | ^7 | ^8"
+        "phpunit/phpunit": "^6 | ^7 | ^8 | ^9"
     },
     "require-dev": {
         "amphp/amp": "^2",

test/AsyncTestCaseTest.php

@@ -132,7 +132,14 @@ public function testSetMinimumRunTime(): \Generator
         };
 
         $this->expectException(AssertionFailedError::class);
-        $this->expectExceptionMessageRegExp("/Expected test to take at least 100ms but instead took (\d+)ms/");
+        $pattern = "/Expected test to take at least 100ms but instead took (\d+)ms/";
+        if (\method_exists($this, 'expectExceptionMessageMatches')) {
+            // PHPUnit 8+
+            $this->expectExceptionMessageMatches($pattern);
+        } else {
+            // PHPUnit 6-7
+            $this->expectExceptionMessageRegExp($pattern);
+        }
         yield call($func);
     }