use variables in test_simplest_plugin

avoids updating hardcoded paths when they change

integration-tests/test_simplest_plugin.py

@@ -4,6 +4,7 @@ Test simplest plugin
 from ruamel.yaml import YAML
 import os
 import subprocess
+from tljh.config import CONFIG_FILE, USER_ENV_PREFIX
 
 yaml = YAML(typ='rt')
 
@@ -20,7 +21,7 @@ def test_pip_packages():
     Test extra user pip packages are installed
     """
     subprocess.check_call([
-        '/opt/tljh/user/bin/python3',
+        f'{USER_ENV_PREFIX}/bin/python3',
         '-c',
         'import django'
     ])
@@ -31,7 +32,7 @@ def test_conda_packages():
     Test extra user conda packages are installed
     """
     subprocess.check_call([
-        '/opt/tljh/user/bin/python3',
+        f'{USER_ENV_PREFIX}/bin/python3',
         '-c',
         'import hypothesis'
     ])
@@ -41,7 +42,7 @@ def test_config_hook():
     """
     Check config changes are present
     """
-    with open('/opt/tljh/config.yaml') as f:
+    with open(CONFIG_FILE) as f:
         data = yaml.load(f)
 
     assert data['simplest_plugin']['present']