Packages: add endpoint to fetch all customers with access to the package

Author: glaubinix

Diff for: README.md

@@ -170,6 +170,12 @@ Returns a new job.
 $client->packages()->remove('acme-website/package');
 ```
 
+##### List all customers with access to a package
+```php
+$client->packages()->listCustomers('acme-website/package');
+```
+Returns a list of customers with access to the package.
+
 #### Credential
 
 ##### List an organization's credentials

Diff for: src/Api/Packages.php

@@ -60,4 +60,9 @@ public function remove($packageName)
     {
         return $this->delete(sprintf('/packages/%s/', $packageName));
     }
+
+    public function listCustomers($packageName)
+    {
+        return $this->get(sprintf('/packages/%s/customers/', $packageName));
+    }
 }

Diff for: tests/Api/PackagesTest.php

@@ -162,6 +162,33 @@ public function testRemove()
         $this->assertSame($expected, $api->remove('acme-website/package'));
     }
 
+    public function testListPackages()
+    {
+        $expected = [
+            [
+                'package' => [
+                    'name' => 'composer/composer',
+                    'origin' => 'private',
+                    'versionConstraint' => null,
+                    'expirationDate' => null,
+                ],
+                'customer' => [
+                    'id' => 1,
+                    'name' => 'Customer',
+                ],
+            ]
+        ];
+
+        /** @var Customers&\PHPUnit_Framework_MockObject_MockObject $api */
+        $api = $this->getApiMock();
+        $api->expects($this->once())
+            ->method('get')
+            ->with($this->equalTo('/packages/composer/composer/customers/'))
+            ->will($this->returnValue($expected));
+
+        $this->assertSame($expected, $api->listCustomers('composer/composer'));
+    }
+
     protected function getApiClass()
     {
         return Packages::class;