some python test cases don't care about backend, so run them in any case

run_project_tests.py

@@ -939,7 +939,7 @@ def detect_tests_to_run(only: T.List[str], use_tmp: bool) -> T.List[T.Tuple[str,
         # CUDA tests on Windows: use Ninja backend:  python run_project_tests.py --only cuda --backend ninja
         TestCategory('cuda', 'cuda', backend not in (Backend.ninja, Backend.xcode) or not shutil.which('nvcc')),
         TestCategory('python3', 'python3', backend is not Backend.ninja),
-        TestCategory('python', 'python', backend is not Backend.ninja),
+        TestCategory('python', 'python'),
         TestCategory('fpga', 'fpga', shutil.which('yosys') is None),
         TestCategory('frameworks', 'frameworks'),
         TestCategory('nasm', 'nasm'),

test cases/python/2 extmodule/meson.build

@@ -3,6 +3,10 @@ project('Python extension module', 'c',
 # Because Windows Python ships only with optimized libs,
 # we must build this project the same way.
 
+if meson.backend() != 'ninja'
+  error('MESON_SKIP_TEST: Ninja backend required')
+endif
+
 py_mod = import('python')
 py = py_mod.find_installation()
 py_dep = py.dependency()

test cases/python/3 cython/meson.build

@@ -1,20 +1,27 @@
 project('cython', 'c',
   default_options : ['warning_level=3'])
 
-cython = find_program('cython3', required : false)
-py3_dep = dependency('python3', required : false)
+if meson.backend() != 'ninja'
+  error('MESON_SKIP_TEST: Ninja backend required')
+endif
 
-if cython.found() and py3_dep.found()
-  py_mod = import('python')
-  py3 = py_mod.find_installation()
-  py3_dep = py3.dependency()
-  subdir('libdir')
+cython = find_program('cython', required : false)
+if not cython.found()
+  error('MESON_SKIP_TEST: Cython3 not found.')
+endif
 
-  test('cython tester',
-    py3,
-    args : files('cytest.py'),
-    env : ['PYTHONPATH=' + pydir]
-  )
-else
-  error('MESON_SKIP_TEST: Cython3 or Python3 libraries not found, skipping test.')
+py3_dep = dependency('python3', required : false)
+if not py3_dep.found()
+  error('MESON_SKIP_TEST: Python library not found.')
 endif
+
+py_mod = import('python')
+py3 = py_mod.find_installation()
+py3_dep = py3.dependency()
+subdir('libdir')
+
+test('cython tester',
+  py3,
+  args : files('cytest.py'),
+  env : ['PYTHONPATH=' + pydir]
+)

test cases/python/4 custom target depends extmodule/meson.build

@@ -3,6 +3,10 @@ project('Python extension module', 'c',
 # Because Windows Python ships only with optimized libs,
 # we must build this project the same way.
 
+if meson.backend() != 'ninja'
+  error('MESON_SKIP_TEST: Ninja backend required')
+endif
+
 py_mod = import('python')
 py3 = py_mod.find_installation()
 py3_dep = py3.dependency(required : false)