[UNVERIFIED-needs-MATLAB] test: skip MATLAB runtime tests when no MATLAB is installed

[ChrisRackauckas-Claude]

Root cause

On master, test/runtests.jl (lines 12-44) unconditionally ran the runtime ODE-solving tests:

sol = solve(prob, MATLABDiffEq.ode45())

solve reaches __solve at src/MATLABDiffEq.jl:118, which calls put_variable(get_default_msession(), ...). get_default_msession() constructs a MATLAB.MSession, which does ccall(eng_open[], ...) (MATLAB/engine.jl:48).

When no MATLAB is installed (every CI runner here, since there is no MATLAB license), MATLAB.jl is built with dummy deps (libmx_size == 0, the documented CI/AutoMerge path in MATLAB.jl's deps/build.jl). With libmx_size == 0, MATLAB.jl's __init__ deliberately skips binding all the engine/mxarray function-pointer Refs (if libmx_size > 0 ... end). So eng_open[] is an unassigned Ref{Ptr{Cvoid}}, and dereferencing it throws:

ERROR: LoadError: UndefRefError: access to undefined reference
  [1] MATLAB.MSession(...)        @ MATLAB engine.jl:48
  [3] get_default_msession        @ MATLAB engine.jl:124
  [4] __solve                     @ MATLABDiffEq src/MATLABDiffEq.jl:118
  ...                             @ test/runtests.jl:20
ERROR: Package MATLABDiffEq errored during testing

This is not a MATLAB.jl API regression and not a ModelingToolkit v11 glue bug: the modelingtoolkitize + build_function(::MATLABTarget()) code generation at lines 107-115 runs fine on ModelingToolkit v11.26.8 / Symbolics v7.26.0. The failure is solely that the suite tries to open a MATLAB engine that does not exist.

Fix

Gate the runtime ODE-solving tests on a real MATLAB being present, using MATLAB.libmx_size > 0 — the exact flag MATLAB.jl itself uses to decide whether to load its native libraries. When MATLAB is present the tests run for real (now with explicit @test assertions on the returned solution, which the old code lacked). When absent, they are skipped with an informative @info message. The MATLAB-free interface and JET/static-analysis tests always run.

No assertions were loosened, skipped, @test_broken-ed, or wrapped in error-swallowing try/catch. The runtime tests are gated on a genuine environment-capability flag, not silenced.

What was verified

Reproduced and fixed locally with an isolated depot on Julia 1.10.11, with CI=true so MATLAB.jl builds the dummy deps exactly as on CI (no MATLAB on the machine).

• Unmodified master (reproduction): suite errors at test/runtests.jl:20 with UndefRefError (matches the failing CI logs). Interface (40/40) and Static Analysis (38/38) testsets passed before the error.
• With this fix: suite passes.

  [ Info: No MATLAB installation detected (MATLAB.libmx_size == 0); skipping the MATLAB runtime solving tests...
  Test Summary:           | Pass  Total  Time
  Interface Compatibility |   40     40  0.1s
  Test Summary:         | Pass  Total  Time
  Static Analysis Tests |   38     38  0.8s
  Testing MATLABDiffEq tests passed
  

What could NOT be verified

There is no MATLAB on this machine, so the HAS_MATLAB == true branch (the actual ODE solves and their new assertions) was not executed. That path is unchanged in behavior from the original tests aside from the added @tests; it still needs a run on a machine with a MATLAB license to confirm end-to-end. Marking this PR UNVERIFIED-needs-MATLAB for that reason.

Runic: ran the Runic.jl formatter on test/runtests.jl (already formatted, no changes).

Ignore until reviewed by @ChrisRackauckas.

🤖 Generated with Claude Code