lint: check-tests-true: Allow #:tests? #t for some build systems.

emacs-build-system sets #:tests? #f by default, so the linter shouldn't warn
if #:tests? #t is set for packages using emacs-build-system.  Likewise for
texlive-build-system.

* guix/lint.scm (check-tests-true): Do not warn if the build system
  is emacs-build-system or texlive-build-system.
* tests/lint.scm
  ("tests-true: #:tests? #t acceptable for emacs packages")
  ("tests-true: #:tests? #t acceptable for texlive packages"): New tests.

Fixes: <https://issues.guix.gnu.org/50299>
Reported-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>
Signed-off-by: Maxim Cournoyer <maxim.cournoyer@gmail.com>

tests/lint.scm

@@ -35,6 +35,8 @@
   #:use-module (guix tests http)
   #:use-module (guix download)
   #:use-module (guix git-download)
+  #:use-module (guix build-system texlive)
+  #:use-module (guix build-system emacs)
   #:use-module (guix build-system gnu)
   #:use-module (guix packages)
   #:use-module (guix lint)
@@ -338,6 +340,25 @@
                              `(#:tests? ,(not (%current-target-system)))))))
     (check-tests-true pkg)))
 
+;; The emacs-build-system sets #:tests? #f by default.
+(test-equal "tests-true: #:tests? #t acceptable for emacs packages"
+  '()
+  (let ((pkg (dummy-package "x"
+                            (build-system emacs-build-system)
+                            (arguments
+                             `(#:tests? #t)))))
+    (check-tests-true pkg)))
+
+;; Likewise, though the 'check' phase is deleted by default,
+;; so #:tests? #t won't be useful by itself.
+(test-equal "tests-true: #:tests? #t acceptable for texlive packages"
+  '()
+  (let ((pkg (dummy-package "x"
+                            (build-system texlive-build-system)
+                            (arguments
+                             `(#:tests? #t)))))
+    (check-tests-true pkg)))
+
 (test-equal "inputs: pkg-config is probably a native input"
   "'pkg-config' should probably be a native input"
   (single-lint-warning-message