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0026 One IronPython Unittest Flow, Dialect 2.7 And 3.4

Date: 2026-08-30

Status

Accepted (shipped). Engine selection matches script execution — pyRevit first, embedded IronPython 3.4.2 otherwise. The pipeline (collect, wire, in-engine runner, test source) runs on IronPython 2.7 and 3.4.2.

Context

RevitDevTool runs Python on two unrelated runtimes.

ExecutionMode.Python uses Python.NET / CPython. In-host tests go through the pytest bridge (tests/run, RevitDevTool.PyTest). pytest 9 cannot run on IronPython.

ExecutionMode.IronPython (*_ipy_script.py) already has one execution flow: RevitIPyExecutionStrategy uses pyRevit Labs/PyRevitLoader when loaded, else embedded IronPython 3.4.2. pyRevit clones may be IronPython 2.7 or 3.x. That auto-pick is the product IronPython runtime, not a second test product.

unittest.main() already executes on the embedded path (ModuleName = "__main__"), but SystemExitException is reported as success. pyRevit IsSuccessResultCode treats Succeeded = 0 and SysExited = 1 as success. A failing suite currently reports success on both backends.

unittest.TestCase is not a runtime signal: the same form already runs on CPython via pytest. A file named test_*_ipy_script.py is collected by pytest test_*.py and executed on Python.NET.

Review judgments: do not pin embedded vs pyrevit as two test protocols; keep one _ipy flow; design the pipeline for 2.7 and 3.4.2 because the engine behind that flow is whichever IronPython execution would use.

Decision

  1. One IronPython flow, same engine policy as scripts. Tests reuse RevitIPyExecutionStrategy (and AutoCAD's embedded IPy where pyRevit does not exist). No engine= request field, no *_pyrevit_test.py, no test-only override of pyRevit-first. Which engine ran may be echoed in diagnostics; it is not a selector.

  2. Pytest collect may use test_*_ipy.py; the host does not. Local pytest needs a fail-closed way to split CPython tests/run from IronPython ipytests/run without importing the module. Filename test_*_ipy.py is that client convention (pytest test_ plus an _ipy marker). It is not a runtime identity: ipytests/run runs unittest on the requested paths. unittest.TestCase is the in-engine runner, not the classifier.

    Pattern (pytest collect) Runtime Protocol
    test_*.py excluding test_*_ipy.py CPython.NET pytest tests/run
    test_*_ipy.py IronPython unittest ipytests/run
    *_ipy_script.py execution-tree script not a test file

    A test_*_ipy.py file that is not unittest.TestCase is a collection error on the client. Ordinary test_*.py stays on CPython pytest. Production / library modules must not use test_*_ipy.py — that name exists only so pytest can route.

  3. The IPy pipeline is a 2.7 / 3.4.2 intersection. Anything executed inside the IronPython engine — user tests and any hosted runner snippet — must parse and run on both. Forbidden in that dialect: f-strings, async/await, type annotations that 2.7 cannot parse, the print x statement (use print(x) — valid on 2.7 and 3.4 without __future__), pytest fixtures, PEP 723, CPython-only stdlib. Prefer driving unittest from C# (DLR / pyRevit script path) so the runner itself is not a Python 3 file.

  4. RevitDevTool.PyTest may expand as collect/report shell only. Intercept test_*_ipy.py (pytest_collect_file), build nodeids without importing the module in CPython, dispatch on ipytests/run. Do not send those files through tests/run / pytest.main().

  5. Local collect must not assume Python 3. Do not import IPy test files. Do not rely on ast.parse (Python 3). Use filename plus a 2/3-safe scan (tokenize / line patterns) for unittest.TestCase and test_*. If per-test names cannot be recovered, one nodeid = the file (whole-file suite). That is the compatible default, not a failure.

  6. tests/run stays CPython + Python.NET. Do not overload PytestRunner.py. Python testing never enters the MTP kernel.

  7. *_ipy_script.py remains script execution. A __main__ unittest self-check is allowed. SystemExit / pyRevit SysExited must yield a truthful ExecutionResult.

Alternatives Considered

  1. Two pinned engines (test_*_ipy.py vs *_pyrevit_test.py). Rejected after review. Duplicates a distinction the execution tree already resolves, and authors would maintain two suites for one product flow.

  2. IronPython stays scripts-only. Rejected. Automated collect/report through the existing pytest client is still wanted; engine count is what collapsed, not the client shell.

  3. Identify IPy tests by unittest.TestCase or a pytest marker. Rejected as primary identity. Filename _ipy is fail-closed and matches _ipy_script.py.

  4. Route test_*_ipy.py through tests/run. Rejected. Host pytest.main() cannot run on IronPython 2.7 or 3.4.

  5. Fold into MTP. Rejected (0021, 0024).

  6. Author tests in Python 3.4-only and skip 2.7. Rejected. pyRevit-first means 2.7 is in the production path on many machines.

Consequences

Positive:

  • one _ipy contract for scripts and tests;
  • pytest IDE tree can list IPy tests without executing them on Python.NET;
  • CPython PytestContracts stay a single mirror;
  • tests exercise the same engine users get when they run *_ipy_script.py.

Tradeoffs:

  • results differ across machines (pyRevit present vs only 3.4.2); that is accepted as matching script execution, and should be visible in the run diagnostic;
  • test source is stuck on the 2.7/3.4 intersection — no f-strings, no pytest fixtures;
  • per-test nodeids may be unavailable when the file is 2.7-only; whole-file suites are first-class;
  • host needs an IronPython unittest runner plus ipytests/run;
  • truthful SystemExit mapping remains a defect fix on both backends.

Follow-Up

  • Spike: SystemExitException on 3.4.2 and pyRevit SysExited vs a failed unittest exit code — both backends, one flow.
  • Spike: selected test ids vs whole-file on the pyRevit script-path API; whole-file is the compatible v1 if selection cannot be 2.7-safe.
  • Plugin: collect test_*_ipy.py without CPython import; 2/3-safe scan.
  • IPy scripts stay *_ipy_script.py (no test_ prefix) so pytest does not collect them.
  • After accept: product layer docs/product/execution.md — one _ipy authoring dialect. One layer only.