Initial implementation of exiftool command, #691 (#696)

* Initial implementation of exiftool command, #691

* updated comment [skip ci]

tests/test_configoptions.py

@@ -1,6 +1,8 @@
 """ test ConfigOptions class """
 
 import pathlib
+from io import StringIO
+
 import pytest
 import toml
 
@@ -43,6 +45,15 @@ def test_write_to_file_load_from_file(tmpdir):
     assert cfg2.bar
 
 
+def test_load_from_str(tmpdir):
+    cfg = ConfigOptions("test", VARS)
+    cfg.bar = True
+    cfg_str = cfg.write_to_str()
+    cfg2 = ConfigOptions("test", VARS).load_from_str(cfg_str)
+    assert cfg2.foo == "bar"
+    assert cfg2.bar
+
+
 def test_load_from_file_error(tmpdir):
     cfg_file = pathlib.Path(str(tmpdir)) / "test.toml"
     cfg = ConfigOptions("test", VARS)