Exception based testing
noexcept(true)andnoexcept(false)noexcept(sizeof(T) <= SmallObjectsSize)- A
trueis used to enable argument that is more performant but would be unsafe in the presence of exceptions - Wide contract: no preconditions
- Narrow contract: has preconditions
- When a preconditon is violated - undefined behavior
Lakos Rule
- We not declare function with a narrow contract noexcept
- Even if we know it will never throw
- Instead we document that it does not throw
Test a precondition check without throwing on failure
child threads
- Spawn test in child thread
- Assert saves info and locks/freezes thread
- Drawbacks
- leaks mmeory
- invalidates RAII
- leaks one thread per test case
“stackful coroutines”
- Assert fail yields to cooperative scheduler / event loop
- Event look calls next test
- Drawbacks
- leaks memory
- invalidates RAII
- unbounded growth of call stack
- nontrivial to construct
- no experience in real world code
Signals
- Just a callback mechanism
- Doesn’t solve the problem of leaving function
Fork based death tests
- Launch each test in a forked process
- assert fail terminates process
- Drawbacks
- requires fast, reliable fork() - UNIX-like systems only!
- can return only 8 bits of diagnostic data
- not widely available in unit test frameworks - Gtest only!
Clone based death tests
- More stable than fork-based
- Drawbacks
- Linux only
Spawn based death tests
- Drawbacks
- Requires external framework (DejaGNU)
- Requires moving test into other source file
- requires buildng state for each test from scratch
- slow
Defensive software framework
- Assert-like macroses to check pre/post condition or invariant
- A way to turn checks on and off
- A user settable way to controlwhat happens when a violation is detected
Possible actions for user-supplied violation handler
- Log the error and continue
- Terminate the program
- Trigger a breakpoint in the debugger
- Executing an endless loop (halt the thread)
- Throw an exception
Takeaways
- Test your preconditions
- Effective to prevent the introduction of bugs across API boundaries due to contract violations
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Best method: Excption-based testing (throw on contract violation)
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Requires that functions with preconditons are not noexcept (“Lakos Rule”)
- Only viable alternative to exception based testing: Death tests . But:
- Much more complex
- Much slower
- Only works on some specific platforms