[PROPOSAL] Add more tests to the library (#865)

* phpunit: use dedicate `Tests` namespace for tests

* tests: replace phpunit with orchestra/testbench

* phpunit: ignore result cache file

* phpunit: adapt test for newer version

* tests: add base testcase class with a helper to run/assert commands

* tests: add test for ide-helper:eloquent

* travis: add global default variables

* travis: disable xdebug, speeds up running tests

* travis: convert php versions to build matrix for environment vars

* travis: only run phpcs/phpunit when the env vars signal it

However phpcs only runs with one test combination from the matrix,
not necessary to execute it every time.

tests/MethodTest.php

@@ -1,8 +1,11 @@
 <?php
 
-namespace Barryvdh\LaravelIdeHelper;
+namespace Barryvdh\LaravelIdeHelper\Tests;
 
-class ExampleTest extends \PHPUnit_Framework_TestCase
+use Barryvdh\LaravelIdeHelper\Method;
+use PHPUnit\Framework\TestCase;
+
+class ExampleTest extends TestCase
 {
     /**
      * Test that we can actually instantiate the class