build-system/pyproject: Always run tests verbosely for supported backends.

* guix/build-system/pyproject.scm (pyproject-build): Default to '() instead of
 #false for TEST-FLAGS.
* guix/build/pyproject-build-system.scm (check): Unconditionally enable
verbose test flags.
* doc/guix.texi (Build Systems): Document this change.
* gnu/packages/fontutils.scm (python-glyphslib)[arguments]: Remove verbosity
from #:test-flags.
* gnu/packages/pdf.scm (python-pydyf, weasyprint)[arguments]: Likewise.
* gnu/packages/python-web.scm (python-openapi-spec-validator)[arguments]: Likewise.
* gnu/packages/python-xyz.scm (python-path, python-tempora)[arguments]: Likewise.

doc/guix.texi

@@ -9332,8 +9332,9 @@ to guess the appropriate backend based on @file{pyproject.toml}.
 @code{#:test-backend} is added.  It defaults to @code{#false} and will guess
 an appropriate test backend based on what is available in package inputs.
 @item
-@code{#:test-flags} is added.  The default is @code{#false}, and varies based
-on the detected @code{#:test-backend}.
+@code{#:test-flags} is added.  The default is @code{'()}.  These flags are
+passed as arguments to the test command.  Note that flags for verbose output
+is always enabled on supported backends.
 @end itemize
 
 It is considered ``experimental'' in that the implementation details are

gnu/packages/fontutils.scm

@@ -598,8 +598,7 @@ (define-public python-glyphslib
     (build-system pyproject-build-system)
     (arguments
      (list
-      #:test-flags #~'("-vv"
-                       ;; These fail because the test data has not yet been
+      #:test-flags #~'(;; These fail because the test data has not yet been
                        ;; updated for newer FontTools:
                        ;;   https://github.com/googlefonts/glyphsLib/issues/787
                        ;; Re-enable for versions > 6.0.7.

gnu/packages/pdf.scm

@@ -739,7 +739,7 @@ (define-public python-pydyf
     (build-system pyproject-build-system)
     (arguments
      (list
-      #:test-flags #~'("-vv" "-c" "/dev/null")))
+      #:test-flags #~'("-c" "/dev/null")))
     (propagated-inputs (list python-pillow))
     (native-inputs
      (list ghostscript
@@ -1500,7 +1500,7 @@ (define-public weasyprint
     (build-system pyproject-build-system)
     (arguments
      (list
-      #:test-flags #~(list "-vv" "-c" "/dev/null"
+      #:test-flags #~(list "-c" "/dev/null"
                            "-n" (number->string (parallel-job-count)))
       #:phases
       #~(modify-phases %standard-phases

gnu/packages/python-web.scm

@@ -1648,7 +1648,7 @@ (define-public python-openapi-spec-validator
      (list
       ;; The example tests attempt to fetch resources from the Internet
       ;; (see: https://github.com/p1c2u/openapi-spec-validator/issues/151).
-      #:test-flags #~'("-vv" "-k" "not Example and not Exampe")
+      #:test-flags #~'("-k" "not Example and not Exampe")
       #:phases
       #~(modify-phases %standard-phases
           (add-after 'unpack 'remove-coverage-pytest-options

gnu/packages/python-xyz.scm

@@ -12753,7 +12753,7 @@ (define-public python-path
        ((#:tests? _ #f)
         (not (%current-target-system)))
        ((#:test-flags flags #~'())
-        #~(append (list "-vv" "-k"
+        #~(append (list "-k"
                         (string-append
                          ;; Do not test the myproject.toml build as it tries
                          ;; to pull dependencies from the Internet.
@@ -21366,7 +21366,7 @@ (define-public python-tempora
     (arguments
      ;; Do not test the myproject.toml build as it tries to pull
      ;; dependencies from the Internet.
-     (list #:test-flags #~'("-vv" "-k" "not project")))
+     (list #:test-flags #~'("-k" "not project")))
     (native-inputs
      (list python-freezegun
            python-pytest

guix/build-system/pyproject.scm

@@ -95,7 +95,7 @@ (define* (pyproject-build name inputs
                           (configure-flags ''())
                           (build-backend #f)
                           (test-backend #f)
-                          (test-flags #f)
+                          (test-flags ''())
                           (phases '%standard-phases)
                           (outputs '("out" "wheel"))
                           (search-paths '())

guix/build/pyproject-build-system.scm

@@ -158,14 +158,16 @@ (define* (check #:key tests? test-backend test-flags #:allow-other-keys)
         (format #t "Using ~a~%" use-test-backend)
         (match use-test-backend
           ('pytest
-           (apply invoke (cons pytest (or test-flags '("-vv")))))
+           (apply invoke pytest "-vv" test-flags))
           ('nose
-           (apply invoke (cons nosetests (or test-flags '("-v")))))
+           (apply invoke nosetests "-v" test-flags))
           ('nose2
-           (apply invoke (cons nose2 (or test-flags '("-v" "--pretty-assert")))))
+           (apply invoke nose2 "-v" "--pretty-assert" test-flags))
           ('setup.py
-           (apply invoke (append '("python" "setup.py")
-                                 (or test-flags '("test" "-v")))))
+           (apply invoke "python" "setup.py"
+                  (if (null? test-flags)
+                      '("test" "-v")
+                      test-flags)))
           ;; The developer should explicitly disable tests in this case.
           (else (raise (condition (&test-system-not-found))))))
       (format #t "test suite not run~%")))