This commits changes WC_Unit_Test_Case parent class to WP_HTTP_TestCase (which extends WP_UnitTestCase). This way all WC core test classes can benefit from the functionality provided by WP_HTTP_TestCase if needed. This is necessary because otherwise test classes can use the functionality provided by WC_Unit_Test_Case or WP_HTTP_TestCase. This change should not affect test classes that don't explicitly call one of the WP_HTTP_TestCase features.
Doing this to speed up the test as an HTTP request to an external server is slow and also because it should fix this test that has been failing on Travis only for an unknown reason.
WP test suite starts a transaction when the test starts and roll it back when the test finishes. So it is not necessary to undo database changes using tearDown().
This commit changes the WC_Tests_Product_CSV_Importer class to use artificial HTTP responses instead of performing real HTTP requests to a external server to get the images of the imported products. On my local machine, this change reduced the test execution time from 3257ms to 831ms.
As a consequence of this change, this commit also fixes WC_Tests_Product_CSV_Importer::test_import() in all Travis builds. This test has been failing for a few weeks on Travis but not on our local environments. After some debugging, I found out that the test was failing on Travis because of the following error when `wp_safe_remote_get()` was called to get images for the imported products:
```
Error getting remote image http://demo.woothemes.com/woocommerce/wp-content/uploads/sites/56/2013/06/T_1_front.jpg. Error: cURL error 35: gnutls_handshake() failed: Handshake failed.
```
Apparently, the PHP binary that is used by Travis is unable to handle the TLS handshake (see https://github.com/travis-ci/travis-ci/issues/6339) and the test probably started failing when demo.woothemes.com (which is used to download the images for the imported products) switched from HTTP to HTTPS.
[According to the WooCommerce wiki](https://github.com/woocommerce/woocommerce/wiki/Order-and-Order-Line-Item-Data) and `WC_REST_Orders_Controller`, WooCommerce stores country codes using the ISO 3166-1 alpha-2 (2 character) standard. However, the `WC_Tests_Order_Functions::test_wc_get_order_address_params()` test method was using 'USA' instead of 'US'.
As @claudiosanches pointed out, there isn't much real-world need for `WC_Install::get_tables()` to sort results. Instead, sort the returned value within the `WC_Tests_Install::test_get_tables()` method.
Since custom tables can be registered within WooCommerce via the 'woocommerce_install_get_tables' filter, it's helpful to ensure that `WC_Install::get_tables()` automatically sorts the table names alphabetically.
This helps avoid false failures when testing a plugin that uses a custom table against the WooCommerce core test suite, as queries like `WC_Tests_Install::test_get_tables()` assumes that tables will be returned in alphabetical order.
Rodrigo Primo
Gerhard Potgieter
Claudiu Lodromanean
Mike Jolley
Jeremy Pry
Khan M Rashedun-Naby
Peter Fabian
Steve Grunwell
