DRY out getting the project version in tests

We were previously getting the version in three different tests. It
makes more sense to turn getting the project version into a fixture and
to use that fixture anywhere the project version is needed.

tests/conftest.py

@@ -10,6 +10,8 @@
 MAIN_SERVICE_NAME = "example"
 VERSION_SERVICE_NAME = f"{MAIN_SERVICE_NAME}-version"
 
+VERSION_FILE = "src/version.txt"
+
 
 @pytest.fixture(scope="session")
 def dockerc():
@@ -36,6 +38,14 @@ def version_container(dockerc):
     return dockerc.compose.ps(services=[VERSION_SERVICE_NAME], all=True)[0]
 
 
+@pytest.fixture(scope="session")
+def project_version():
+    """Return the version of the project."""
+    with open(VERSION_FILE) as f:
+        project_version = f.read().strip()
+    return project_version
+
+
 def pytest_addoption(parser):
     """Add new commandline options to pytest."""
     parser.addoption(

tests/container_test.py

@@ -60,31 +60,25 @@ def test_output(dockerc, main_container):
 @pytest.mark.skipif(
     RELEASE_TAG in [None, ""], reason="this is not a release (RELEASE_TAG not set)"
 )
-def test_release_version():
+def test_release_version(project_version):
     """Verify that release tag version agrees with the module version."""
-    with open(VERSION_FILE) as f:
-        project_version = f.read().strip()
     assert (
         RELEASE_TAG == f"v{project_version}"
     ), "RELEASE_TAG does not match the project version"
 
 
-def test_log_version(dockerc, version_container):
+def test_log_version(dockerc, project_version, version_container):
     """Verify the container outputs the correct version to the logs."""
     # make sure container exited if running test isolated
     dockerc.wait(version_container.id)
     log_output = version_container.logs().strip()
-    with open(VERSION_FILE) as f:
-        project_version = f.read().strip()
     assert (
         log_output == project_version
     ), f"Container version output to log does not match project version file {VERSION_FILE}"
 
 
-def test_container_version_label_matches(version_container):
+def test_container_version_label_matches(project_version, version_container):
     """Verify the container version label is the correct version."""
-    with open(VERSION_FILE) as f:
-        project_version = f.read().strip()
     assert (
         version_container.config.labels["org.opencontainers.image.version"]
         == project_version