mock-acme

The integration between the mocks. mock-sap, mock-edi and mock-bank stand in for systems you do not own, so that the code between them can be tested. This is that code: ACME's middleware, the fourth actor in every story the mocks tell.

It is not a mock, and it is not a client library to put in front of real money. It is a reference: worked integrations, each with tests that run against the released mocks, kept in one place so that there is one copy of each.

What is here

mockacme.bank_messages is what the two payment modules share: the call to the bank and the reading of its ISO 20022 answers.

Every module talks to the mocks over HTTP and imports none of them. The package has no dependencies.

Installing

python3 -m pip install mock-acme

That installs the package and nothing else. The mocks it talks to are separate: pip install mock-sap mock-edi mock-bank.

payment_run needs mock-sap 0.19.0 or later. It writes which payment run has an invoice on the invoice itself, which an older mock-sap refuses, so nothing is paid. And against an older one, a customer's payment that quotes the number of an invoice already paid reopens that invoice.

Running the tests

From a checkout:

python3 -m pip install -e ".[test]"
python3 -m unittest discover -s tests -t . -v

That is the whole arrangement. Importing tests starts the three mocks, each on a port the operating system chose, and stops them afterwards. tests/__init__.py says how to point the tests at a mock that is already running, which is how they are run against a mock's main.

tests/test_payment_run_readers.py is the one test that imports a mock rather than talking to it: it gives payment_run's hand-written statement readers the same statement mock-bank wrote as a camt.053 and as BAI2, and five BAI2 files from moov-io/bai2, and holds them to mock-bank's own reader. The samples and their licence are in tests/samples/external/.

payment_run pays by ACH as well. The same tests in that mode:

PAYMENT_RUN_FORMAT=nacha python3 -m unittest -v tests.test_payment_run

The released mocks are what a pull request is tested against. A second workflow, mocks-main.yml, runs the same tests every night against each mock's main, so that a change merged there which breaks this code is seen before it is released. It is not a required check; a red run there says something about another repository. To do the same by hand:

python3 -m pip install \
  "mock-sap @ git+https://github.com/rseufert/mock-sap@main" \
  "mock-edi @ git+https://github.com/rseufert/mock-edi@main" \
  "mock-bank @ git+https://github.com/rseufert/mock-bank@main"

Known to be wrong

Two payment runs that select at the same moment can both pay an invoice. A run says in SAP which run has each item before its file goes out, as PaymentRunID and PaymentRunDate on the invoice, and every other run leaves that item alone until the bank refuses the payment, SAP clears it, or the payment comes back (#2, #21). But reading the open items and writing the claim are two requests, and nothing makes them one: two runs that both read before either writes both pay. One run after another, on any machine, is safe; two at once are not.

It has other edges:

• A run's identification is one to six characters, which is SAP's own limit. A longer one is refused before anything is selected.
• When the bank refuses a payment and SAP cannot then be reached, the claim stays on the item and no run selects it. The run says so as a problem, and a person has to take the claim off.
• Register, the run's own record from before SAP could hold this, is still accepted and no longer needed. Passing one means two records of one fact: whoever posts the statements has to be given the same register, or its entry outlives the claim and holds an item SAP says is free.

Money arriving is posted to SAP and nothing comes of it. Each credit on the statement says whether it is a payment coming back or money arriving, so SAP no longer takes a receipt for a return, but posting it against a receivable is not built (mock-sap#65). SAP answers the line as unprocessed, and that is on the statement's record.

Releasing

A release is the same three acts as in the mocks, by one person in one sitting: merge a pull request that sets version in pyproject.toml and __version__ in mockacme/__init__.py and dates the section in CHANGELOG.md; tag that commit v<version>; publish a GitHub Release from the tag. Publishing the Release runs publish.yml, which runs the tests, builds, refuses a tag that disagrees with the package, and uploads to PyPI through Trusted Publishing. Running that workflow by hand uploads to TestPyPI instead.

There is no tools/release.py here as there is in the mocks: the steps are done by hand, and CI checks only that the two places the version is written agree.

Where the code came from

The modules were copied on 2026-10-04 from the examples/ folder of the mock each was written beside, with their tests; remittance was written there afterwards and followed on 2026-10-05. Nothing in them changed but imports, the lines saying how to run the tests, and issue references, which now name the repository they belong to.

The originals were removed from those repositories on 2026-10-05, and each left an examples/README.md saying which file became which. This is the only copy.

The repository's settings are described in docs/GITHUB.md.