tests: consolidate mock scope creation logic in conftest.py

Config scopes were different for `config` and `mutable_config`,
and `mutable_config` did not have a command line scope.

- [x] Fix by consolidating the creation logic for the two fixtures.

lib/spack/spack/test/bootstrap.py

@@ -103,16 +103,8 @@ def test_bootstrap_search_for_compilers_with_environment_active(
 
 @pytest.mark.regression('26189')
 def test_config_yaml_is_preserved_during_bootstrap(mutable_config):
-    # Mock the command line scope
     expected_dir = '/tmp/test'
-    internal_scope = spack.config.InternalConfigScope(
-        name='command_line', data={
-            'config': {
-                'test_stage': expected_dir
-            }
-        }
-    )
-    spack.config.config.push_scope(internal_scope)
+    spack.config.set("config:test_stage", expected_dir, scope="command_line")
 
     assert spack.config.get('config:test_stage') == expected_dir
     with spack.bootstrap.ensure_bootstrap_configuration():

lib/spack/spack/test/conftest.py

@@ -612,19 +612,23 @@ def configuration_dir(tmpdir_factory, linux_os):
     shutil.rmtree(str(tmpdir))
 
 
+def _create_mock_configuration_scopes(configuration_dir):
+    """Create the configuration scopes used in `config` and `mutable_config`."""
+    scopes = [
+        spack.config.InternalConfigScope('_builtin', spack.config.config_defaults),
+    ]
+    scopes += [
+        spack.config.ConfigScope(name, str(configuration_dir.join(name)))
+        for name in ['site', 'system', 'user']
+    ]
+    scopes += [spack.config.InternalConfigScope('command_line')]
+    return scopes
+
+
 @pytest.fixture(scope='session')
 def mock_configuration_scopes(configuration_dir):
     """Create a persistent Configuration object from the configuration_dir."""
-    defaults = spack.config.InternalConfigScope(
-        '_builtin', spack.config.config_defaults
-    )
-    test_scopes = [defaults]
-    test_scopes += [
-        spack.config.ConfigScope(name, str(configuration_dir.join(name)))
-        for name in ['site', 'system', 'user']]
-    test_scopes.append(spack.config.InternalConfigScope('command_line'))
-
-    yield test_scopes
+    yield _create_mock_configuration_scopes(configuration_dir)
 
 
 @pytest.fixture(scope='function')
@@ -640,9 +644,7 @@ def mutable_config(tmpdir_factory, configuration_dir):
     mutable_dir = tmpdir_factory.mktemp('mutable_config').join('tmp')
     configuration_dir.copy(mutable_dir)
 
-    scopes = [spack.config.ConfigScope(name, str(mutable_dir.join(name)))
-              for name in ['site', 'system', 'user']]
-
+    scopes = _create_mock_configuration_scopes(mutable_dir)
     with spack.config.use_configuration(*scopes) as cfg:
         yield cfg
 
@@ -662,6 +664,8 @@ def mutable_empty_config(tmpdir_factory, configuration_dir):
 def no_compilers_yaml(mutable_config):
     """Creates a temporary configuration without compilers.yaml"""
     for scope, local_config in mutable_config.scopes.items():
+        if not local_config.path:  # skip internal scopes
+            continue
         compilers_yaml = os.path.join(local_config.path, 'compilers.yaml')
         if os.path.exists(compilers_yaml):
             os.remove(compilers_yaml)