[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.

composer.json

@@ -22,9 +22,9 @@
         "illuminate/config": "^5.5|^6",
         "illuminate/view": "^5.5|^6",
         "phpro/grumphp": "^0.14",
-        "phpunit/phpunit" : "4.*",
         "scrutinizer/ocular": "~1.1",
-        "squizlabs/php_codesniffer": "^3"
+        "squizlabs/php_codesniffer": "^3",
+        "orchestra/testbench": "^4.4"
     },
     "autoload": {
         "psr-4": {
@@ -33,7 +33,7 @@
     },
     "autoload-dev": {
         "psr-4": {
-            "Barryvdh\\LaravelIdeHelper\\": "tests"
+            "Barryvdh\\LaravelIdeHelper\\Tests\\": "tests"
         }
     },
     "scripts": {