improvements to test

- check that "* dev23a" is somewhere in the string (not required to be in the
first line)

- create local variables before we run the assert statement. The can be
inspected when calling `py.test -l` (or `py.test --pdb`).

- improve documentation of what we expect

tests.py

@@ -89,17 +89,19 @@ def test_prepare_environment(tmp_path):
     assert release_base_dir.exists()
     # check for spack-environments directory
     assert spack_environments in os.listdir(release_base_dir)
-    # check if the git branch is correctly checked out
-    assert (
+
+    # check if the git branch is correctly checked out. We expect output such as
+    # git_branch_stdout = '* dev-23a\n  develop\n'
+    # The entry with the '* ' prefix is the active branch.
+    git_branch_output_raw = \
         subprocess.run(
             f"cd {str(release_base_dir/spack_environments)} && git branch",
             shell=True,
             capture_output=True,
         )
-        .stdout.decode("utf-8")
-        .split("\n")[0]
-        == f"* {mpsd_release_to_test}"
-    )
+    git_branch_stdout = git_branch_output_raw.stdout.decode("utf-8")
+    assert f"* {mpsd_release_to_test}" in git_branch_stdout
+
     # check that result is a list and contains atleast ['global','foss2021a-mpi']
     assert isinstance(result, list)
     assert "global" in result