Fix handling of tox 4 provision without tox minversion

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=2240590

The added test actually blows up without the fix with both tox 4 or tox 3,
so perhaps this bug also existed with tox 3.

pyproject-rpm-macros.spec

@@ -183,8 +183,10 @@ export HOSTNAME="rpmbuild"  # to speedup tox in network-less mock, see rhbz#1856
 
 
 %changelog
-* Wed Sep 13 2023 Karolina Surma <ksurma@redhat.com> - 1.10.0-1
+* Wed Sep 13 2023 Python Maint <python-maint@redhat.com> - 1.10.0-1
 - Add %%_pyproject_check_import_allow_no_modules for automated environments
+- Fix handling of tox 4 provision without and explicit tox minversion
+- Fixes: rhbz#2240590
 
 * Wed May 31 2023 Maxwell G <maxwell@gtmx.me> - 1.9.0-1
 - Allow passing config_settings to the build backend.

pyproject_buildrequires.py

@@ -386,7 +386,7 @@ def generate_tox_requirements(toxenv, requirements):
         provision_content = provision.read()
         if provision_content and r.returncode != 0:
             provision_requires = json.loads(provision_content)
-            if 'minversion' in provision_requires:
+            if provision_requires.get('minversion') is not None:
                 requirements.add(f'tox >= {provision_requires["minversion"]}',
                                  source='tox provision (minversion)')
             if 'requires' in provision_requires:

pyproject_buildrequires_testcases.yaml

@@ -589,6 +589,43 @@ tox provision satisfied:
       python3dist(inst)
   result: 0
 
+tox provision no minversion:
+  installed:
+    setuptools: 50
+    wheel: 1
+    tox: 3.5.3
+    tox-current-env: 0.0.6
+  toxenv:
+    - py3
+  setup.py: |
+    from setuptools import setup
+    setup(
+        name='test',
+        version='0.1',
+    )
+  tox.ini: |
+    [tox]
+    requires =
+        setuptools > 40
+        wheel > 2
+  expected:
+    - |  # tox 3
+      python3dist(setuptools) >= 40.8
+      python3dist(wheel)
+      python3dist(wheel)
+      python3dist(tox-current-env) >= 0.0.6
+      python3dist(setuptools) > 40.0
+      python3dist(wheel) > 2.0
+    - |  # tox 4
+      python3dist(setuptools) >= 40.8
+      python3dist(wheel)
+      python3dist(wheel)
+      python3dist(tox-current-env) >= 0.0.6
+      python3dist(setuptools) > 40.0
+      python3dist(wheel) > 2.0
+      python3dist(tox)
+  result: 0
+
 Default build system, unmet deps in requirements file:
   installed:
     setuptools: 50