diff --git .travis.yml .travis.yml
index a7460eeae..428391d2a 100644
--- .travis.yml
+++ .travis.yml
@@ -61,7 +61,9 @@ before_script:
 - phpenv versions
 - npm --version
 - node --version
-script: grunt $WP_TRAVISCI
+script:
+- grunt $WP_TRAVISCI
+- if [ "$TRAVIS_BRANCH" == "master" ]; then grunt phpunit:trunk-only; fi
 notifications:
   slack:
     rooms:
diff --git Gruntfile.js Gruntfile.js
index 4323fce81..12a03fe04 100644
--- Gruntfile.js
+++ Gruntfile.js
@@ -437,6 +437,10 @@ module.exports = function(grunt) {
 			'external-http': {
 				cmd: 'phpunit',
 				args: ['-c', 'phpunit.xml.dist', '--group', 'external-http']
+			},
+			'trunk-only': {
+				cmd: 'phpunit',
+				args: ['-c', 'phpunit.xml.dist', '--group', 'trunk-only']
 			}
 		},
 		uglify: {
diff --git phpunit.xml.dist phpunit.xml.dist
index 415ec7699..6a089b7ea 100644
--- phpunit.xml.dist
+++ phpunit.xml.dist
@@ -1,51 +1,52 @@
-<phpunit
-	bootstrap="tests/phpunit/includes/bootstrap.php"
-        backupGlobals="false"
-        colors="true"
-        >
-    <testsuites>
-        <!-- Default test suite to run all tests -->
-        <testsuite>
-            <directory suffix=".php">tests/phpunit/tests</directory>
-            <exclude>tests/phpunit/tests/actions/closures.php</exclude>
-            <exclude>tests/phpunit/tests/image/editor.php</exclude>
-            <exclude>tests/phpunit/tests/image/editor_gd.php</exclude>
-            <exclude>tests/phpunit/tests/image/editor_imagick.php</exclude>
-            <exclude>tests/phpunit/tests/oembed/headers.php</exclude>
-            <file phpVersion="5.3.0">tests/phpunit/tests/actions/closures.php</file>
-            <file phpVersion="5.3.0">tests/phpunit/tests/image/editor.php</file>
-            <file phpVersion="5.3.0">tests/phpunit/tests/image/editor_gd.php</file>
-            <file phpVersion="5.3.0">tests/phpunit/tests/image/editor_imagick.php</file>
-            <file phpVersion="5.3.0">tests/phpunit/tests/oembed/headers.php</file>
-        </testsuite>
-    </testsuites>
-    <groups>
-        <exclude>
-            <group>ajax</group>
-            <group>ms-files</group>
-            <group>external-http</group>
-        </exclude>
-    </groups>
-    <logging>
-        <log type="junit" target="tests/phpunit/build/logs/junit.xml" logIncompleteSkipped="false"/>
-    </logging>
-    <php>
-        <const name="WP_RUN_CORE_TESTS" value="1" />
-    </php>
-	<listeners>
-		<listener class="SpeedTrapListener" file="tests/phpunit/includes/speed-trap-listener.php">
-			<arguments>
-				<array>
-					<element key="slowThreshold">
-						<integer>150</integer>
-					</element>
-				</array>
-			</arguments>
-		</listener>
-	</listeners>
-	<filter>
-		<whitelist processUncoveredFilesFromWhitelist="true">
-			<directory suffix=".php">src</directory>
-		</whitelist>
-	</filter>
-</phpunit>
+<phpunit
+	bootstrap="tests/phpunit/includes/bootstrap.php"
+		backupGlobals="false"
+		colors="true"
+		>
+	<testsuites>
+		<!-- Default test suite to run all tests -->
+		<testsuite>
+			<directory suffix=".php">tests/phpunit/tests</directory>
+			<exclude>tests/phpunit/tests/actions/closures.php</exclude>
+			<exclude>tests/phpunit/tests/image/editor.php</exclude>
+			<exclude>tests/phpunit/tests/image/editor_gd.php</exclude>
+			<exclude>tests/phpunit/tests/image/editor_imagick.php</exclude>
+			<exclude>tests/phpunit/tests/oembed/headers.php</exclude>
+			<file phpVersion="5.3.0">tests/phpunit/tests/actions/closures.php</file>
+			<file phpVersion="5.3.0">tests/phpunit/tests/image/editor.php</file>
+			<file phpVersion="5.3.0">tests/phpunit/tests/image/editor_gd.php</file>
+			<file phpVersion="5.3.0">tests/phpunit/tests/image/editor_imagick.php</file>
+			<file phpVersion="5.3.0">tests/phpunit/tests/oembed/headers.php</file>
+		</testsuite>
+	</testsuites>
+	<groups>
+		<exclude>
+			<group>ajax</group>
+			<group>ms-files</group>
+			<group>external-http</group>
+			<group>trunk-only</group>
+		</exclude>
+	</groups>
+	<logging>
+		<log type="junit" target="tests/phpunit/build/logs/junit.xml" logIncompleteSkipped="false"/>
+	</logging>
+	<php>
+		<const name="WP_RUN_CORE_TESTS" value="1" />
+	</php>
+	<listeners>
+		<listener class="SpeedTrapListener" file="tests/phpunit/includes/speed-trap-listener.php">
+			<arguments>
+				<array>
+					<element key="slowThreshold">
+						<integer>150</integer>
+					</element>
+				</array>
+			</arguments>
+		</listener>
+	</listeners>
+	<filter>
+		<whitelist processUncoveredFilesFromWhitelist="true">
+			<directory suffix=".php">src</directory>
+		</whitelist>
+	</filter>
+</phpunit>
diff --git tests/phpunit/includes/bootstrap.php tests/phpunit/includes/bootstrap.php
index 6ddc3f612..4048a9903 100644
--- tests/phpunit/includes/bootstrap.php
+++ tests/phpunit/includes/bootstrap.php
@@ -133,6 +133,7 @@ class WP_PHPUnit_Util_Getopt extends PHPUnit_Util_Getopt {
 			'ajax' => true,
 			'ms-files' => true,
 			'external-http' => true,
+			'trunk-only' => true,
 		);
 
 		foreach ( $options as $option ) {
diff --git tests/phpunit/multisite.xml tests/phpunit/multisite.xml
index f30452f1c..9207d1f4b 100644
--- tests/phpunit/multisite.xml
+++ tests/phpunit/multisite.xml
@@ -26,6 +26,7 @@
             <group>ms-files</group>
             <group>external-http</group>
             <group>oembed-headers</group>
+            <group>trunk-only</group>
         </exclude>
     </groups>
     <php>
diff --git tests/phpunit/tests/external-http/basic.php tests/phpunit/tests/external-http/basic.php
index 70439caf4..8e068273e 100644
--- tests/phpunit/tests/external-http/basic.php
+++ tests/phpunit/tests/external-http/basic.php
@@ -4,6 +4,9 @@
  */
 class Tests_External_HTTP_Basic extends WP_UnitTestCase {
 
+	/**
+	 * @group trunk-only
+	 */
 	function test_readme() {
 		$readme = file_get_contents( ABSPATH . 'readme.html' );
 		preg_match( '#<br /> Version (.*)#', $readme, $matches );