[RFC PATCH 2/9] tests: add "TESTS_PYTHON" variable to Makefile

[John Snow <jsnow@redhat.com>]

This is a convenience feature: $(PYTHON) points to the Python executable
we were instructed to use by the configure script. We use that Python to
create a virtual environment with the "check-venv" target in
tests/Makefile.include.

$(TESTS_PYTHON) points to the Python executable belonging to the virtual
environment tied to the build. This Python executable is a symlink to
the binary used to create the venv, which will be the version provided
at configure time.

Using $(TESTS_PYTHON) therefore uses the $(PYTHON) executable, but with
paths modified to use packages installed to the venv.

Signed-off-by: John Snow <jsnow@redhat.com>
---
 tests/Makefile.include | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tests/Makefile.include b/tests/Makefile.include
index ec84b2ebc04..146aaa96a00 100644
--- a/tests/Makefile.include
+++ b/tests/Makefile.include
@@ -89,6 +89,7 @@ TARGETS=$(patsubst libqemu-%.fa, %, $(filter libqemu-%.fa, $(ninja-targets)))
 TESTS_VENV_DIR=$(BUILD_DIR)/tests/venv
 TESTS_VENV_REQ=$(SRC_PATH)/tests/requirements.txt
 TESTS_RESULTS_DIR=$(BUILD_DIR)/tests/results
+TESTS_PYTHON=$(TESTS_VENV_DIR)/bin/python
 ifndef AVOCADO_TESTS
 	AVOCADO_TESTS=tests/avocado
 endif
@@ -108,7 +109,7 @@ $(TESTS_VENV_DIR): $(TESTS_VENV_REQ)
             $(PYTHON) -m venv $@, \
             VENV, $@)
 	$(call quiet-command, \
-            $(TESTS_VENV_DIR)/bin/python -m pip -q install -r $(TESTS_VENV_REQ), \
+            $(TESTS_PYTHON) -m pip -q install -r $(TESTS_VENV_REQ), \
             PIP, $(TESTS_VENV_REQ))
 	$(call quiet-command, touch $@)
 
@@ -126,7 +127,7 @@ FEDORA_31_DOWNLOAD=$(filter $(FEDORA_31_ARCHES),$(FEDORA_31_ARCHES_CANDIDATES))
 # download one specific Fedora 31 image
 get-vm-image-fedora-31-%: check-venv
 	$(call quiet-command, \
-             $(TESTS_VENV_DIR)/bin/python -m avocado vmimage get \
+             $(TESTS_PYTHON) -m avocado vmimage get \
              --distro=fedora --distro-version=31 --arch=$*, \
 	"AVOCADO", "Downloading avocado tests VM image for $*")
 
@@ -135,7 +136,7 @@ get-vm-images: check-venv $(patsubst %,get-vm-image-fedora-31-%, $(FEDORA_31_DOW
 
 check-avocado: check-venv $(TESTS_RESULTS_DIR) get-vm-images
 	$(call quiet-command, \
-            $(TESTS_VENV_DIR)/bin/python -m avocado \
+            $(TESTS_PYTHON) -m avocado \
             --show=$(AVOCADO_SHOW) run --job-results-dir=$(TESTS_RESULTS_DIR) \
             $(if $(AVOCADO_TAGS),, --filter-by-tags-include-empty \
 			--filter-by-tags-include-empty-key) \
-- 
2.34.1