Configurable extra arguments to go test

ADD:
  - layers/+lang/go/config.el Added new variable `go-use-test-args` to allow
    specifying additional arguments being passed to `go test.

CHANGE:
  - layers/+lang/go/packages.el Updated `go-run-tests` to automatically concat
    the new variable `go-use-test-args` to args passed to `go test`.

layers/+lang/go/README.org

@@ -103,6 +103,11 @@ Tests are run in a compilation buffer displayed in a popup window that can be
 closed by pressing ~C-g~ from any other window. The variable
 =go-test-buffer-name= can be customized to set the output buffer name.
 
+To provide additional arguments to go test, specify =go-use-test-args=.
+#+begin_src emacs-lisp
+  (go :variables go-use-test-args "-race -timeout 10s"
+#+end_src
+
 ** Guru
 
 Go Oracle has been deprecated as of October 1, 2016, it's replacement is =go-guru=.

layers/+lang/go/config.el

@@ -24,3 +24,6 @@
 
 (defvar go-test-buffer-name "*go test*"
   "Name of the buffer for go test output. Default is *go test*.")
+
+(defvar go-use-test-args ""
+  "Additional arguments to be supplied to `go test` during runtime.")

layers/+lang/go/packages.el

@@ -65,7 +65,8 @@
 
       (defun spacemacs/go-run-tests (args)
         (interactive)
-        (compilation-start (concat "go test " args) nil (lambda (n) go-test-buffer-name) nil))
+        (compilation-start (concat "go test " args " " go-use-test-args)
+                           nil (lambda (n) go-test-buffer-name) nil))
 
       (defun spacemacs/go-run-package-tests ()
         (interactive)