split one test into three

(I am trying to debug the third one on the Mac, and this makes it easier.)

mpsd-software-environment.py

@@ -258,14 +258,15 @@ def create_dir_structure(mpsd_release: str, script_dir: Path) -> None:
         with os_chdir("spack-environments"):
             # Git fetch and checkout the release branch and git pull
             # to be sure that the resulting repo is up to date
-            run(["git", "fetch", "--all"])
-            checkout_result = run(["git", "checkout", mpsd_release])
+            run(["git", "fetch", "--all"], check=True)
+            checkout_result = run(["git", "checkout", mpsd_release], check=True)
+
             if checkout_result.returncode != 0:
                 raise Exception(
                     "Release branch does not exist in spack-environment repo \n."
                     "Check for typos."
                 )
-            run(["git", "pull"])
+            run(["git", "pull"], check=True)
 
 
 def get_release_info(mpsd_release: str, script_dir: Path) -> Tuple[str, str, List[str]]:
@@ -306,13 +307,15 @@ def get_release_info(mpsd_release: str, script_dir: Path) -> Tuple[str, str, Lis
         with os_chdir("spack-environments"):
             # Get the branch and commit hash of the spack-environments repo
             spe_commit_hash = (
-                run(["git", "rev-parse", "HEAD"], stdout=subprocess.PIPE)
+                run(["git", "rev-parse", "HEAD"], stdout=subprocess.PIPE, check=True)
                 .stdout.decode()
                 .strip()
             )
             spe_branch = (
                 run(
-                    ["git", "rev-parse", "--abbrev-ref", "HEAD"], stdout=subprocess.PIPE
+                    ["git", "rev-parse", "--abbrev-ref", "HEAD"],
+                    stdout=subprocess.PIPE,
+                    check=True,
                 )
                 .stdout.decode()
                 .strip()