Makefile: init (#2351)

The idea of this file is to make it easier to run tests. It will ensure
that the tests are running with the correct NIX_PATH (pointing it to
e.g.: unstable), and also allowing it to run either one or all tests.

.github/CODEOWNERS

@@ -361,3 +361,5 @@
 /modules/xsession.nix                                 @rycee
 
 /modules/services/volnoti.nix                         @IvanMalison
+
+Makefile                                              @thiagokokada

Makefile

@@ -0,0 +1,13 @@
+.PHONY: all all-tests test
+NIX_PATH := nixpkgs=https://github.com/NixOS/nixpkgs/archive/nixpkgs-unstable.tar.gz
+
+all: all-tests
+
+all-tests:
+	$(MAKE) test TEST=all
+
+test:
+ifndef TEST
+	$(error Use 'make test TEST=<test_name>' to run desired test)
+endif
+	nix-shell --pure tests -I ${NIX_PATH} -A run.${TEST}