Bootstrap Python venv for tests

A number of QEMU tests are written in Python, and may benefit
from an untainted Python venv.

By using make rules, tests that depend on specific Python libs
can set that rule as a requirement, along with rules that require
the presence or installation of specific libraries.

The tests/requirements.txt is supposed to contain the Python
requirements that should be added to the venv created by check-venv.
Signed-off-by: NCleber Rosa <crosa@redhat.com>
Tested-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Acked-by: NStefan Hajnoczi <stefanha@redhat.com>
Acked-by: NWainer dos Santos Moschetta <wainersm@redhat.com>
Reviewed-by: NCaio Carrara <ccarrara@redhat.com>
Message-Id: <20181018153134.8493-2-crosa@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

tests/Makefile.include

@@ -12,6 +12,7 @@ check-help:
 	@echo " $(MAKE) check-block          Run block tests"
 	@echo " $(MAKE) check-tcg            Run TCG tests"
 	@echo " $(MAKE) check-report.html    Generates an HTML test report"
+	@echo " $(MAKE) check-venv           Creates a Python venv for tests"
 	@echo " $(MAKE) check-clean          Clean the tests"
 	@echo
 	@echo "Please note that HTML reports do not regenerate if the unit tests"
@@ -899,6 +900,30 @@ check-decodetree:
           ./check.sh "$(PYTHON)" "$(SRC_PATH)/scripts/decodetree.py", \
           TEST, decodetree.py)
 
+# Python venv for running tests
+
+.PHONY: check-venv
+
+TESTS_VENV_DIR=$(BUILD_DIR)/tests/venv
+TESTS_VENV_REQ=$(SRC_PATH)/tests/requirements.txt
+
+$(shell $(PYTHON) -c 'import sys; assert sys.version_info >= (3,0)' >/dev/null 2>&1)
+ifeq ($(.SHELLSTATUS),0)
+$(TESTS_VENV_DIR): $(TESTS_VENV_REQ)
+	$(call quiet-command, \
+            $(PYTHON) -m venv --system-site-packages $@, \
+            VENV, $@)
+	$(call quiet-command, \
+            $(TESTS_VENV_DIR)/bin/python -m pip -q install -r $(TESTS_VENV_REQ), \
+            PIP, $(TESTS_VENV_REQ))
+	$(call quiet-command, touch $@)
+else
+$(TESTS_VENV_DIR):
+	$(error "venv directory for tests requires Python 3")
+endif
+
+check-venv: $(TESTS_VENV_DIR)
+
 # Consolidated targets
 
 .PHONY: check-qapi-schema check-qtest check-unit check check-clean
@@ -912,6 +937,7 @@ check-clean:
 	rm -rf $(check-unit-y) tests/*.o $(QEMU_IOTESTS_HELPERS-y)
 	rm -rf $(sort $(foreach target,$(SYSEMU_TARGET_LIST), $(check-qtest-$(target)-y)) $(check-qtest-generic-y))
 	rm -f tests/test-qapi-gen-timestamp
+	rm -rf $(TESTS_VENV_DIR)
 
 clean: check-clean
 

tests/requirements.txt

+# Add Python module requirements, one per line, to be installed
+# in the tests/venv Python virtual environment. For more info,
+# refer to: https://pip.pypa.io/en/stable/user_guide/#id1