gnu: python-testpath: Update to 0.5.0 and enable tests.

* gnu/packages/check.scm (python-testpath): Update to 0.5.0.
[phases]{relax-requirements}: New phase
{build}: Build using pypa-build's 'build' command.
{check}: Override phase.
{install}: Adjust.
[native-inputs]: Remove python-flit.  Add python-pypa-build and python-pytest.
[home-page]: Update.

gnu/packages/check.scm

@@ -79,6 +79,7 @@
   #:use-module ((guix licenses) #:prefix license:)
   #:use-module (guix packages)
   #:use-module (guix download)
+  #:use-module (guix gexp)
   #:use-module (guix git-download)
   #:use-module (guix build-system cmake)
   #:use-module (guix build-system glib-or-gtk)
@@ -1865,7 +1866,7 @@ C/C++, R, and more, and uploads it to the @code{codecov.io} service.")
 (define-public python-testpath
   (package
     (name "python-testpath")
-    (version "0.4.4")
+    (version "0.5.0")
     (source
      (origin
        (method git-fetch)
@@ -1875,35 +1876,33 @@ C/C++, R, and more, and uploads it to the @code{codecov.io} service.")
        (file-name (git-file-name name version))
        (sha256
         (base32
-         "1fwv4d3p54xx1x942s104irr35lszvv6jnr4nn1scsfvc0m1qmbk"))))
+         "08r1c6bhvj8pcdvzkqv1950k36a6q3v81fd2p1yqdq3c07mcwgif"))))
     (build-system python-build-system)
     (arguments
-     `(#:tests? #f ; this package does not even have a setup.py
-       #:modules ((guix build python-build-system)
-                  (guix build utils)
-                  (srfi srfi-1))
-       #: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$"))))))))
+     (list
+      #:phases
+      #~(modify-phases %standard-phases
+          (add-after 'unpack 'relax-requirements
+            (lambda _
+              (substitute* "pyproject.toml"
+                (("flit_core >=3.2.0,<3.3")
+                 "flit_core >=3.2.0"))))
+          ;; XXX: PEP 517 manual build copied from python-isort.
+          (replace 'build
+            (lambda _
+              (invoke "python" "-m" "build" "--wheel" "--no-isolation" ".")))
+          (replace 'check
+           (lambda* (#:key tests? #:allow-other-keys)
+             (when tests?
+               (invoke "pytest"))))
+          (replace 'install
+            (lambda _
+              (let ((whl (car (find-files "dist" "\\.whl$"))))
+                (invoke "pip" "--no-cache-dir" "--no-input"
+                        "install" "--no-deps" "--prefix" #$output whl)))))))
     (native-inputs
-     (list python-flit))
-    (home-page "https://github.com/takluyver/testpath")
+     (list python-pypa-build python-flit-core python-pytest))
+    (home-page "https://github.com/jupyter/testpath")
     (synopsis "Test utilities for code working with files and commands")
     (description
      "Testpath is a collection of utilities for Python code working with files