diff --git a/.gitignore b/.gitignore
index bcf211b3..f1616236 100644
--- a/.gitignore
+++ b/.gitignore
@@ -9,3 +9,5 @@ composer.lock
 phpunit.xml
 phpcs.xml
 .phpcs.xml
+.phpunit.cache
+.phpunit.result.cache
diff --git a/phpcs.xml.dist b/phpcs.xml.dist
index e82b67bc..6da9ad35 100644
--- a/phpcs.xml.dist
+++ b/phpcs.xml.dist
@@ -18,7 +18,7 @@
 	<exclude-pattern>*/src/WP_CLI/JsonManipulator\.php$</exclude-pattern>
 	<exclude-pattern>*/src/WP_CLI/Package/Compat/Min_Composer_1_10/NullIOMethodsTrait\.php$</exclude-pattern>
 	<exclude-pattern>*/src/WP_CLI/Package/Compat/Min_Composer_2_3/NullIOMethodsTrait\.php$</exclude-pattern>
-	<exclude-pattern>*/tests/test-json-manipulator\.php$</exclude-pattern>
+	<exclude-pattern>*/tests/JsonManipulatorTest\.php$</exclude-pattern>
 
 	<!-- Show progress. -->
 	<arg value="p"/>
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index bcdd6b1c..dc984734 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,11 +1,20 @@
-<phpunit
-	bootstrap="vendor/autoload.php"
-	colors="true"
-	>
-	<testsuites>
-		<testsuite>
-			<directory prefix="spec-" suffix=".php">tests/</directory>
-			<directory prefix="test-" suffix=".php">tests/</directory>
-		</testsuite>
-	</testsuites>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+		 xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/4.8/phpunit.xsd"
+		 bootstrap="vendor/autoload.php"
+		 backupGlobals="false"
+		 beStrictAboutCoversAnnotation="true"
+		 beStrictAboutOutputDuringTests="true"
+		 beStrictAboutTestsThatDoNotTestAnything="true"
+		 beStrictAboutTodoAnnotatedTests="true"
+		 colors="true"
+		 verbose="true">
+	<testsuite name="wp-cli/package-command tests">
+		<directory suffix="Test.php">tests</directory>
+	</testsuite>
+
+	<filter>
+		<whitelist processUncoveredFilesFromWhitelist="true">
+			<directory suffix=".php">src</directory>
+		</whitelist>
+	</filter>
 </phpunit>
diff --git a/tests/test-composer-json.php b/tests/ComposerJsonTest.php
similarity index 97%
rename from tests/test-composer-json.php
rename to tests/ComposerJsonTest.php
index dcb214c0..82ef7d46 100644
--- a/tests/test-composer-json.php
+++ b/tests/ComposerJsonTest.php
@@ -28,10 +28,10 @@ public function set_up() {
 		WP_CLI::set_logger( $this->logger );
 
 		// Enable exit exception.
+
 		$class_wp_cli_capture_exit = new \ReflectionProperty( 'WP_CLI', 'capture_exit' );
 		$class_wp_cli_capture_exit->setAccessible( true );
-		$this->prev_capture_exit = $class_wp_cli_capture_exit->getValue();
-		$class_wp_cli_capture_exit->setValue( true );
+		$class_wp_cli_capture_exit->setValue( null, true );
 
 		$this->temp_dir = Utils\get_temp_dir() . uniqid( 'wp-cli-test-package-composer-json-', true ) . '/';
 		mkdir( $this->temp_dir );
@@ -44,7 +44,7 @@ public function tear_down() {
 		// Restore exit exception.
 		$class_wp_cli_capture_exit = new \ReflectionProperty( 'WP_CLI', 'capture_exit' );
 		$class_wp_cli_capture_exit->setAccessible( true );
-		$class_wp_cli_capture_exit->setValue( $this->prev_capture_exit );
+		$class_wp_cli_capture_exit->setValue( null, $this->prev_capture_exit );
 
 		rmdir( $this->temp_dir );
 
diff --git a/tests/test-json-manipulator.php b/tests/JsonManipulatorTest.php
similarity index 99%
rename from tests/test-json-manipulator.php
rename to tests/JsonManipulatorTest.php
index add2727a..026f7bec 100644
--- a/tests/test-json-manipulator.php
+++ b/tests/JsonManipulatorTest.php
@@ -26,7 +26,7 @@ public function testAddLink($json, $type, $package, $constraint, $expected)
         $this->assertEquals($expected, $manipulator->getContents());
     }
 
-    public function linkProvider()
+    public static function linkProvider()
     {
         return array(
             array(
@@ -1297,7 +1297,7 @@ public function testAddLinkAndSortPackages($json, $type, $package, $constraint,
         $this->assertEquals($expected, $manipulator->getContents());
     }
 
-    public function providerAddLinkAndSortPackages()
+    public static function providerAddLinkAndSortPackages()
     {
         return array(
             array(
@@ -1380,7 +1380,7 @@ public function testRemoveSubNode($json, $name, $expected, $expectedContent = nu
         }
     }
 
-    public function removeSubNodeProvider()
+    public static function removeSubNodeProvider()
     {
         return array(
             'works on simple ones first' => array(
@@ -2374,7 +2374,7 @@ public function testAddLinkCaseInsensitive($json, $type, $package, $constraint,
         $this->assertEquals($expected, $manipulator->getContents());
     }
 
-    public function providerAddLinkCaseInsensitive()
+    public static function providerAddLinkCaseInsensitive()
     {
         return array(
             array(
@@ -2441,7 +2441,7 @@ public function testAddSubNodeCase($json, $mainNode, $name, $caseInsensitive, $e
 		$this->assertSame($expected, $manipulator->getContents());
     }
 
-    public function providerAddSubNodeCase()
+    public static function providerAddSubNodeCase()
     {
         return array(
             array(
@@ -2504,7 +2504,7 @@ public function testRemoveSubNodeCaseInsensitive($json, $mainNode, $name, $expec
         }
     }
 
-    public function providerRemoveSubNodeCaseInsensitive()
+    public static function providerRemoveSubNodeCaseInsensitive()
     {
         return array(
             array(