import: pypi: Fix tests.

* guix/import/pypi.scm (unzip-command): Use invoke instead of
system*.
(read-wheel-metadata): Adapt accordingly.
(guess-requirements-from-wheel): Improve readability.

* tests/import/pypi.scm (parse-wheel-metadata): Add test (used to
isolate the issue in another test).
(pypi->guix-package, no wheel): Remove python-wheel from the result.
(pypi->guix-package, no usable requirement file, no wheel.): Likewise.
(pypi->guix-package, package name contains \"-\" followed by digits):
Likewise.
(package-latest-release): Likewise.
(pypi->guix-package, no requires.txt, but wheel): Likewise. Also
improve readability.

guix/import/pypi.scm

@@ -303,8 +303,9 @@ not succeed."
                  (mlet* %store-monad
                      ((drv (lower-object unzip))
                       (built (built-derivations (list drv))))
-                   (return (string-append (derivation->output-path drv) "/bin/unzip"))))))))
-    (system* (string-append unzip-cmd (string-join args " " 'prefix)))))
+                   (return (string-append (derivation->output-path drv)
+                                          "/bin/unzip"))))))))
+    (apply invoke unzip-cmd args)))
 
 (define (parse-requires.txt requires.txt)
   "Given REQUIRES.TXT, a path to a Setuptools requires.txt file, return a list
@@ -414,10 +415,9 @@ be extracted in a temporary directory."
            (metadata (string-append dirname "/METADATA")))
       (call-with-temporary-directory
        (lambda (dir)
-         (if (zero?
-              (parameterize ((current-error-port (%make-void-port "rw+"))
-                             (current-output-port (%make-void-port "rw+")))
-                (unzip-command wheel-archive "-d" dir metadata)))
+         (if (parameterize ((current-error-port (%make-void-port "rw+"))
+                            (current-output-port (%make-void-port "rw+")))
+               (unzip-command wheel-archive "-d" dir metadata))
              (parse-wheel-metadata (string-append dir "/" metadata))
              (begin
                (warning
@@ -430,8 +430,7 @@ be extracted in a temporary directory."
     (call-with-temporary-output-file
      (lambda (temp port)
        (if wheel-url
-           (and (url-fetch wheel-url temp)
-                (read-wheel-metadata temp))
+           (and=> (url-fetch wheel-url temp) read-wheel-metadata)
            (list '() '())))))
 
   (define (guess-requirements-from-pyproject.toml dir)

tests/import/pypi.scm

@@ -270,6 +270,12 @@ files specified by SPECS.  Return its file name."
          call-with-input-string)
         (parse-requires.txt test-requires.txt-beaker)))
 
+(test-equal "parse-wheel-metadata"
+  (list '("baz" "bar") '("pytest"))
+  (mock ((ice-9 ports) call-with-input-file
+         call-with-input-string)
+        (parse-wheel-metadata test-metadata)))
+
 (test-equal "parse-wheel-metadata, with extras"
   (list '("wrapt" "bar") '("tox" "bumpversion"))
   (mock ((ice-9 ports) call-with-input-file
@@ -328,8 +334,7 @@ files specified by SPECS.  Return its file name."
             (build-system pyproject-build-system)
             (propagated-inputs (list python-bar python-foo))
             (native-inputs (list python-pytest
-                                 python-setuptools
-                                 python-wheel))
+                                 python-setuptools))
             (home-page "https://example.com")
             (synopsis "summary")
             (description "summary.")
@@ -431,8 +436,7 @@ files specified by SPECS.  Return its file name."
     (with-pypi `(("/foo-1.0.0.tar.gz" 200 ,(file-dump tarball))
                  ("/foo-1.0.0-py2.py3-none-any.whl"
                   200 ,(file-dump wheel))
-                 ("/foo/json" 200 ,(lambda (port)
-                                     (display (foo-json) port))))
+                 ("/foo/json" 200 ,(cut display (foo-json) <>)))
       ;; Not clearing the memoization cache here would mean returning the value
       ;; computed in the previous test.
       (invalidate-memoization! pypi->guix-package)
@@ -448,8 +452,7 @@ files specified by SPECS.  Return its file name."
             (build-system pyproject-build-system)
             (propagated-inputs (list python-bar python-baz))
             (native-inputs (list python-pytest
-                                 python-setuptools
-                                 python-wheel))
+                                 python-setuptools))
             (home-page "https://example.com")
             (synopsis "summary")
             (description "summary.")
@@ -478,7 +481,7 @@ files specified by SPECS.  Return its file name."
                        (sha256
                         (base32 ,(? string? hash)))))
             (build-system pyproject-build-system)
-            (native-inputs (list python-setuptools python-wheel))
+            (native-inputs (list python-setuptools))
             (home-page "https://example.com")
             (synopsis "summary")
             (description "summary.")
@@ -509,8 +512,7 @@ files specified by SPECS.  Return its file name."
             (build-system pyproject-build-system)
             (propagated-inputs (list python-bar python-foo))
             (native-inputs (list python-pytest
-                                 python-setuptools
-                                 python-wheel))
+                                 python-setuptools))
             (home-page "https://example.com")
             (synopsis "summary")
             (description "summary.")
@@ -537,10 +539,6 @@ files specified by SPECS.  Return its file name."
               (upstream-input
                (name "setuptools")
                (downstream-name "python-setuptools")
-               (type 'native))
-              (upstream-input
-               (name "wheel")
-               (downstream-name "python-wheel")
                (type 'native))))
   (let ((tarball (pypi-tarball
                   "foo-1.0.0"