gnu: emacs-yasnippet: Don't use unstable tarball.

* gnu/packages/emacs-xyz.scm (emacs-yasnippet)[source]: Use GIT-FETCH and
  GIT-FILE-NAME.
[source]: Enable tests.

gnu/packages/emacs-xyz.scm

@@ -8325,13 +8325,14 @@ been adapted to work with mu4e.")
     (name "emacs-yasnippet")
     (version "0.13.0")
     (source (origin
-              (method url-fetch)
-              (uri (string-append "https://github.com/joaotavora/yasnippet/"
-                                  "archive/" version ".tar.gz"))
+              (method git-fetch)
+              (uri (git-reference
+                    (url "https://github.com/joaotavora/yasnippet.git")
+                    (commit version)))
               (file-name (string-append name "-" version ".tar.gz"))
               (sha256
                (base32
-                "12ls2x17agzbrj1xynjbmfa11igqxia4hj4fv6fpr66yci2r1plc"))
+                "0fkkplycrw8f8r30hjjxl1wm7p2irq2ipzzc1g7cc52abaal796p"))
               (modules '((guix build utils)))
               (snippet
                '(begin
@@ -8345,6 +8346,28 @@ been adapted to work with mu4e.")
                      "))\n"))
                   #t))))
     (build-system emacs-build-system)
+    (arguments
+     `(#:tests? #t
+       #:test-command '("emacs" "--batch"
+                        "-l" "yasnippet-tests.el"
+                        "-f" "ert-run-tests-batch-and-exit")
+       ;; FIXME: one failing test
+       #:phases
+       (modify-phases %standard-phases
+         (add-before 'check 'make-tests-writable
+           (lambda _
+             (make-file-writable "yasnippet-tests.el")
+             #t))
+         (add-before 'check 'delete-rebinding-test
+           (lambda _
+             (emacs-batch-edit-file "yasnippet-tests.el"
+               `(progn (progn (goto-char (point-min))
+                              (re-search-forward
+                               "ert-deftest test-rebindings")
+                              (beginning-of-line)
+                              (kill-sexp))
+                       (basic-save-buffer)))
+             #t)))))
     (home-page "https://github.com/joaotavora/yasnippet")
     (synopsis "Yet another snippet extension for Emacs")
     (description