pytest nested parametrization with tree-like data

Question

Using pytest, I'm trying to test a tree like hierarchical scenario. Lets use a document structure as an example:

Document --- Chapter --- Paragraph
       1   n        1   n

Where a document contains multiple chapters; a chapter contains multiple paragraphs.

When starting testing a new document, some setup code need to be run; when a new chapter is started, some other setup code need to be run; and the same for paragraph.

Written as pseudo code:

for doc in documents:
    setup_doc(doc)
    for chapter in doc.chapters:
        setup_chapter(chapter)
        for paragraph in chapter.paragraphs:
            setup_paragraph(paragraph)
            test_it(doc, chapter, paragraph)
            teardown_paragraph(paragraph)
        teardown_chapter(chapter)
    teardown_doc(doc)

If we have the following data:

Document Alpha
   chapter A
      Paragraph A1
      Paragraph A2
   chapter B
      Paragraph B1

I would expect the collected test cases to be:

test_it[Alpha, A, A1]
test_it[Alpha, A, A2]
test_it[Alpha, B, B1]

I've tried different combinations of pytest_generate_tests, class scenarios, fixtures and parametrized test functions, but have not been able to achieve this.

Any pointers would be greatly appreciated.

Answer 1

Pytest fixutes are supposed to be independent. So to solve your task you have to build one fixture with plain list of all features combinations (document - chapter - paragraph).

You can do that with simple fixture that returns one element of such a list or you can generate this list on test generation phase as demonstrated in the code below.

documents = {
        'Alpha': {
            'A': {'A1': {},'A2': {}},
            'B': {'B1': {}}
        }
    }


def pytest_generate_tests(metafunc):
    """Documents tree from documents"""
    if 'document' in metafunc.fixturenames:
        documents_plain = []
        for document in documents.keys():
            for chapter in documents[document].keys():
                for paragraph in documents[document][chapter].keys():
                    documents_plain.append({'document': document, 'chapter': chapter, 'paragraph': paragraph})
        metafunc.parametrize(
            'document',
            documents_plain,
            scope='session')


def test_it(document):
    print('{}, {}, {}'.format(document['document'], document['chapter'], document['paragraph']))


py.test -s

Alpha, B, B1
Alpha, A, A1
Alpha, A, A2