Compiler does catch circular dependencies like → mutal import, use, some struct references, etc.
that create a compile order deadlock.
ArchTest catches with should_be_free_of_cycles → Runtime call graph cycles, these are cases where module A calls a function in B, and B calls a function in A.
Elixir compiles these just fine — there’s no compilation deadlock — but they represent tight architectural coupling you might want to prevent.
Example: test fixture and assertion tests
ArchTest isn’t about catching things that won’t compile — it’s about enforcing the architectural rules your team has agreed on, so they don’t quietly erode over time. Things like “the Web layer
should never call into Orders directly”, “no circular dependencies between bounded contexts”, or “no IO.puts left in production code”. The code will compile and run fine without these rules — but six months later you’ve got a ball of mud.
ArchTest makes those rules fail the test suite, so they stay enforced as the codebase grows and new people join the team.