Custom filters and functions

Both functions & filters are a piece of python code, which catcher can run from the template. The algorithm is simple:

1. You create a python file with functions you’d like to run from your tests
2. You point catcher to this file (or files)
3. You use it in your templates
4. Profit.

You can use built-in functions and filters implementation catcher.modules.filter_impl.bifs() as an example.

Functions

Catcher support custom functions to be used in templates.

Important: In order to use your function you should name it starting with function_.

For example function_my_fun will be imported in catcher and can be used as my_fun in templates.

If function doesn’t start with function_ it will be ignored. Although your template’s function_my_fun can still use ignored function itself.

You can have multiple functions in the same python file.

Imagine you have a file /home/user/tests/my_functions.py with content:

def function_my_custom():
   return {'key': 'value'}

def some_other_function(arg):
    return 'converted_to_string: ' + str(arg)

In this case function_my_custom will be imported and you will be able to use my_custom as a function in tests:

---
steps:
    - kafka:
        produce:
            server: '{{ my_kafka }}'
            topic: 'my_topic'
            data: '{{ my_custom() }}'

To make it work you need to tell catcher where your implementation is. Just run it with -f param:

catcher -f /home/user/tests/my_functions.py tests/my_test.yml

You can have multiple params in case you have multiple modules to import: -f <module_1> -f <module_2>

Filters

You can use filters exactly the same way as functions. Please see Jinja2 documentation on what filter is.

Important: In order to use your filter you should name it starting with filter_.

For example: filter_my_filter will be imported in catcher and can be used as my_filter in templates.

If function doesn’t start with filter_ it will be ignored.

You can have both functions and filters in the same python file.

Just add this code to my_functions, so it should look like this:

def function_my_custom():
   return {'key': 'value'}

def filter_increment(input):
   if isinstance(input, int):
     return input + 1
   return 'not an int'

def some_other_function(arg):
    return 'converted_to_string: ' + str(arg)

In this case you have both my_custom function and increment filter available for catcher. Let’s try the filter:

---
steps:
    - postgres:
        request:
            conf: '{{ postgres }}'
            sql: 'select count(*) from test'
        register: {documents: '{{ OUTPUT.count }}'}
    - kafka:
        produce:
            server: '{{ my_kafka }}'
            topic: 'my_topic'
            data: '{{ documents | increment }}'

You can also have filter with parameters:

def filter_encode(input, arg='base64'):
    if arg == 'base64':
        import base64
        return base64.b64encode(input.encode()).decode()
    return str(input)

And call it in test with or without param:

---
steps:
    - mongo:
        request:
            conf: '{{ mongo }}'
            collection: 'test'
            insert_one:
                'user': '{{ username }}'
                'password_urlencoded': '{{ password | encode('base64') }}'
                'password_clean': '{{ password | encode }}'

System functions

If your python module is already installed in the system (and is available via pydoc.locate) - you can just specify it’s

module path.

F.e. my_package/my_module.py.

If it is not installed in the system - specify it as a source file: catcher -f /full/path/to/my_package/my_module.py.

If it was already installed in the system - specify only python path: catcher -f my_package.my_module without py.