split one test into three

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

tests.py

@@ -139,8 +139,8 @@ def test_setup_log_cmd(tmp_path):
         assert "Spack environments branch: dev-23a " in last_line
 
 
-def test_install_environment(tmp_path):
-    # Test the installation part
+def test_install_environment_wrong_toolchain(tmp_path):
+    """Test exception is raised for non-existing toolchain."""
     # This is a long test, its handy to test this with print statements printed to
     # stdout, use:
     #   pytest -s
@@ -151,6 +151,9 @@ def test_install_environment(tmp_path):
             toolchains=["wrong-toolchain"],
             script_dir=(tmp_path),
         )
+
+def test_install_environment_wrong_mpsd_release(tmp_path):
+    """Test exception is raised for non-existing mpsd release."""
     # Expect an Exception when wrong mpsd_release is provided (part of
     # prepare_environment)
     with pytest.raises(Exception):
@@ -159,6 +162,9 @@ def test_install_environment(tmp_path):
             toolchains=["foss2021a-mpi"],
             script_dir=(tmp_path),
         )
+
+def test_install_environment_zlib(tmp_path):
+    """Test installation of toolchain."""
     # prepare a test of global generic with only zlib to test the installation
     # prepare dev-23a release
     # script_dir = tmp_path / "test_global_generic"