test wheel instead of src

makefile

@@ -339,11 +339,13 @@ test:
 		test/ src/;
 
 	# Next we install the package and run the test suite against it.
+	mkdir -p build/test_wheel;
+	$(DEV_ENV_PY) setup.py bdist_wheel --dist-dir build/test_wheel;
 
 	IFS=' ' read -r -a env_paths <<< "$(CONDA_ENV_PATHS)"; \
 	for i in $${!env_paths[@]}; do \
 		env_py=$${env_paths[i]}/bin/python; \
-		$${env_py} -m pip install --upgrade .; \
+		$${env_py} -m pip install --upgrade build/test_wheel/*.whl; \
 		ENV=$${ENV-dev} $${env_py} -m pytest test/; \
 	done;
 

setup.py

@@ -56,7 +56,6 @@ setuptools.setup(
         [console_scripts]
         pycalver=pycalver.__main__:cli
     """,
-    python_requires=">=3.6",
     zip_safe=True,
     classifiers=[
         "Development Status :: 4 - Beta",