Add test(s) for `ABCParse.function_kwargs` 

Could look something like this:

```python
import ABCParse
def test_func(arg1, arg2):
    return arg1, arg2

arg1 = "x"
arg2 = "y"

class TestClass:
    def __init__(self, arg1="x", arg2="y", arg3="z"):
        
        self.kw = ABCParse.function_kwargs(func = test_func, kwargs = locals())
        
tc = TestClass()
tc.kw
```