Consider to implement a more declarative approach for validate_settings. You wrote

Still, I can't think of a better way other than checking each individual key in each individual dictionay/subdictionary, since each key has a different name, each subdict has a different structure and many different data types are used for values.

Of course, but a generic description for this cannot be much more complex than your actual JSON file? Why not have a complementary description file in JSON for those values, for example, like this:

{ "global_settings": { "param1": "integer", "param2": "bool", "param3": "double|optional" }, "simulation_settings": { "param4": "bool", "param5": "bool", "param6": "bool|optional" }, "output_settings": { "file_settings": { "param7": "string" "param8": "bool" "param9": "bool|optional" }, "param10": "bool" } } 

Now, validate_settings can use this description and do the validation for data types and non-optional values in a generic fashion. And that makes the actual testing of validate_settings a whole lot simpler, since for getting full test coverage, you can now use a few simple tests which cover each data type once and the optional/non-optional feature.

Of course, you will also have to proofread the description file to make sure it contains no errors, but that is way less effort than writing a test for each original attribute (and proofread also there is no error in those tests).

Consider to implement a more declarative approach for validate_settings. You wrote

Still, I can't think of a better way other than checking each individual key in each individual dictionay/subdictionary, since each key has a different name, each subdict has a different structure and many different data types are used for values.

I can think of one. I guess a generic description for the settings cannot be much more complex than your actual JSON file? Why not have a complementary description file in JSON for those values, for example, like this:

{ "global_settings": { "param1": "integer", "param2": "bool", "param3": "double|optional" }, "simulation_settings": { "param4": "bool", "param5": "bool", "param6": "bool|optional" }, "output_settings": { "file_settings": { "param7": "string" "param8": "bool" "param9": "bool|optional" }, "param10": "bool" } } 

Now, validate_settings can use this description and do the validation for data types and non-optional values in a generic fashion. And that makes the actual testing of validate_settings a whole lot simpler, since for getting full test coverage, you can now use a few simple tests which cover each data type once and the optional/non-optional feature.

Of course, you will also have to proofread the description file to make sure it contains no errors, but that is way less effort than writing a test for each original attribute (and proofread also there is no error in those tests).

As an alternative, you could also have a look at JSON schema, which seems to be way more powerful, but I am not an expert on this.