force `subprocess.run` to check return code is 0

In general, this should help to capture unintentional errors.

Where the change has created failures, they have been fixed. (Mostly because the git repository that was looked for was missing.)

tests.py

@@ -31,18 +31,36 @@ def test_prepare_environment(tmp_path):
     # prepare_env is run when cmd is not specified, we can test cmd='prepare'
     # and cmd=None to check both cases
 
-    script_dir = tmp_path / "test_prepare_env"
+    script_dir = tmp_path / "mpsd_opt" / "linux_debian_11"
     spack_environments = "spack-environments"
     mpsd_release_to_test = "dev-23a"
     release_base_dir = script_dir / mpsd_release_to_test
     # check that the test directory does not exist
     assert not script_dir.exists()
 
+    # prepare_environment expects to be executed in git repository
+    # (mpsd-software-environments). It queries the commit on which we are to
+    # log that information. For this to work, we need to execute the command
+    # within a directory tree that has a git repository at the same or high
+    # level. Let's create one:
+
+    # create directory first
+    script_dir.mkdir(parents=True)
+    # then create git repository:
+    with mod.os_chdir(str(script_dir)):
+        subprocess.run("git init .", shell=True, check=True)
+        subprocess.run("echo 'fake content' > readme.txt", shell=True, check=True)
+        subprocess.run("git add readme.txt", shell=True, check=True)
+        subprocess.run("pwd", shell=True)
+        subprocess.run(
+            'git commit -m "first commit" readme.txt', shell=True, check=True
+        )
+
+    # now call the function we want to test
     result = mod.prepare_environment(
-        mpsd_release=mpsd_release_to_test, script_dir=(script_dir)
+        mpsd_release=mpsd_release_to_test, script_dir=script_dir
     )
-    # wait for 20 seconds for the git clone to finish
-    # time.sleep(20)
+
     # check if the directory now is created
     assert release_base_dir.exists()
     # check for spack-environments directory