Testing Lambda Functions that reference modules included in a layer

Question

I've been working a on a CRUD SAM application using a Python 3.8 runtime. My lambda functions reference a lambda layer that has code shared amongst the functions. My application builds/deploys and I can invoke the functions locally, however, in composing unit tests (using pytest), I'm not sure how to get around my imports referencing a layer in line that doesn't match the file structure.

File structure:

.
├── template.yaml
├── _layer-folder
│   └── _python
│       └── shared_code.py 
├── _lambda
│   ├── some_function.py
│   └── _tests
│       └── test-some-function.py

When running my tests for my lambda functions, I get an import error when I reference a module in that lives in the shared layer. For example:

from some_module_in_a_layer import some_layer_function

Is there a way to configure pytest to reference the correct file directory when running the tests?

dev_bri · Accepted Answer · 2021-08-30 20:04:15Z

3

I ended up resolving this by appending to the system path when testing or running locally within my __init__.py file.

if os.environ.get("ENVIRONMENT") == "test":
    sys.path.append(os.getcwd() + '/path/to/layer')

answered Aug 30, 2021 at 20:04

dev_bri

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LRutten · Accepted Answer · 2021-08-27 10:33:49Z

0

It's a pain indeed to test layers properly and it kind of depends on your method of running the test (e.g. in Pycharm or using the terminal). In PyCharm you can add the layers directory as a source (right click use as source). To run from terminal you can add it to your PYTHONPATH before running, but it's quite ugly. So PYTHONPATH='/path/to/layer' python main.py

It's not pretty but I don't know another way to fix that tbh.

answered Aug 27, 2021 at 10:33

LRutten

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1 Comment

dev_bri Over a year ago

I appreciate the response!

Remotec · Accepted Answer · 2022-11-03 15:06:51Z

0

I added this line in my test and it worked perfectly.

test_file.py

import pytest

sys.path.append(os.getcwd() + '/../layer_location')

Inside layer location my file system looks like this:

layer-location\
  __init__.py
  layer_code.py

The import in my non-test code is then:

code_under_test.py

from layer_code import foo

foo()

answered Nov 3, 2022 at 15:06

Remotec

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