Use versioned pytest executable in `%pytest` macro for non-main Python stack

macros.python3

@@ -73,7 +73,7 @@
 }
 
 # This is intended for Python 3 only, hence also no Python version in the name.
-%__pytest /usr/bin/pytest
+%__pytest /usr/bin/pytest%(test %{python3_pkgversion} == 3 || echo -%{python3_version})
 %pytest %{expand:\\\
   CFLAGS="${CFLAGS:-${RPM_OPT_FLAGS}}" LDFLAGS="${LDFLAGS:-${RPM_LD_FLAGS}}"\\\
   PATH="%{buildroot}%{_bindir}:$PATH"\\\

tests/test_evals.py

@@ -188,6 +188,13 @@ def test_pytest_different_command():
     assert 'pytest-3' in lines[-1]
 
 
+def test_pytest_command_suffix():
+    lines = rpm_eval('%pytest -v')
+    assert '/usr/bin/pytest -v' in lines[-1]
+    lines = rpm_eval('%pytest -v', python3_pkgversion="3.6", python3_version="3.6")
+    assert '/usr/bin/pytest-3.6 -v' in lines[-1]
+
+
 def test_pypi_source_default_name():
     url = rpm_eval('%pypi_source',
                    name='foo', version='6')[0]