gnu: python-tinycss2: Enable tests.

* gnu/packages/python-web.scm (python-tinycss2)[source]: Fetch from git
repository to include tests.
[arguments]: Build from source with flit.
[native-inputs]: Add python-flit, python-pytest, python-pytest-cov,
python-pytest-flake8, and python-pytest-isort.

gnu/packages/python-web.scm

@@ -4563,18 +4563,47 @@ (define-public python-tinycss2
     (version "1.1.0")
     (source
      (origin
-       (method url-fetch)
-       (uri (pypi-uri "tinycss2" version))
+       (method git-fetch)
+       (uri (git-reference
+             (url "https://github.com/Kozea/tinycss2")
+             (commit (string-append "v" version))
+             (recursive? #true)))
+       (file-name (git-file-name name version))
        (sha256
-        (base32 "12p16k8x8ig51gpfcwz3k3kxpxrwwkn41a1avdgvh3nn8hqarp7v"))))
+        (base32 "0zyc48vbmczpqj7f3f0d7zb3bz29fyj50dg0m6bbwbr5i88kq3sq"))))
     (build-system python-build-system)
     (arguments
-     ;; Test data is missing from the PyPI archive, and the build system is
-     ;; based on Flit, which wants an unmaintained and unpackaged
-     ;; python-pytoml dependency.
-     `(#:tests? #f))
+     `(#:phases
+       (modify-phases %standard-phases
+         (replace 'build
+           (lambda _
+             ;; A ZIP archive should be generated, but it fails with "ZIP does
+             ;; not support timestamps before 1980".  Luckily,
+             ;; SOURCE_DATE_EPOCH is respected, which we set to some time in
+             ;; 1980.
+             (setenv "SOURCE_DATE_EPOCH" "315532800")
+             (invoke "flit" "build")))
+         (replace 'install
+           (lambda* (#:key inputs outputs #:allow-other-keys)
+             (add-installed-pythonpath inputs outputs)
+             (let ((out (assoc-ref outputs "out")))
+               (for-each (lambda (wheel)
+                           (format #true wheel)
+                           (invoke "python" "-m" "pip" "install"
+                                   wheel (string-append "--prefix=" out)))
+                         (find-files "dist" "\\.whl$")))))
+         (replace 'check
+           (lambda* (#:key inputs outputs tests? #:allow-other-keys)
+             (add-installed-pythonpath inputs outputs)
+             (invoke "pytest" "-vv"))))))
     (propagated-inputs
      `(("python-webencodings" ,python-webencodings)))
+    (native-inputs
+     `(("python-flit" ,python-flit)
+       ("python-pytest" ,python-pytest)
+       ("python-pytest-cov" ,python-pytest-cov)
+       ("python-pytest-flake8" ,python-pytest-flake8)
+       ("python-pytest-isort" ,python-pytest-isort)))
     (home-page "https://tinycss2.readthedocs.io/")
     (synopsis "Low-level CSS parser for Python")
     (description "@code{tinycss2} can parse strings, return Python objects