RandomWordsEQOracle fails with empty automaton

[windmueller]

When a RandomWordsEQOracle is queried with an empty hypothesis automaton, an exception is thrown:

java.lang.ArrayIndexOutOfBoundsException: -2
    at net.automatalib.automata.base.compact.AbstractCompactDeterministic.getTransition(AbstractCompactDeterministic.java:161)
    at net.automatalib.automata.base.compact.AbstractCompactDeterministic.getTransition(AbstractCompactDeterministic.java:170)
    at net.automatalib.automata.base.compact.AbstractCompactDeterministic.getTransition(AbstractCompactDeterministic.java:32)
    at net.automatalib.ts.abstractimpl.AbstractDeterministicTransOutTS.trace(AbstractDeterministicTransOutTS.java:30)
    at net.automatalib.automata.transout.impl.compact.CompactMealy.trace(CompactMealy.java:99)
    at net.automatalib.automata.transout.impl.compact.CompactMealy.trace(CompactMealy.java:33)
    at net.automatalib.ts.abstractimpl.AbstractDeterministicTransOutTS.trace(AbstractDeterministicTransOutTS.java:22)
    at net.automatalib.automata.transout.impl.compact.CompactMealy.trace(CompactMealy.java:90)
    at net.automatalib.automata.transout.abstractimpl.AbstractTransOutAutomaton.computeOutput(AbstractTransOutAutomaton.java:37)
    at net.automatalib.automata.transout.impl.compact.CompactMealy.computeOutput(CompactMealy.java:117)
    at net.automatalib.automata.transout.impl.compact.CompactMealy.computeOutput(CompactMealy.java:33)
    at de.learnlib.eqtests.basic.RandomWordsEQOracle.findCounterExample(RandomWordsEQOracle.java:105)
    at de.learnlib.eqtests.basic.RandomWordsEQOracle$MealyRandomWordsEQOracle.findCounterExample(RandomWordsEQOracle.java:49)
    at de.learnlib.eqtests.basic.RandomWordsEQOracleTest.testEmptyAutomaton(RandomWordsEQOracleTest.java:32)

This can be tested on the branch "eqTestEmptyAutomaton" in RandomWordsEQOracleTest

[mtf90]

What behavior would you expect? Any interaction with an unitialized automaton (i.e. with no defined initial state) is ill-defined.

Imo, the only improvement could be, to not let this error sink through to the automaton level, but to but check for the undefinedness and throw an IllegalArgumentException.

[windmueller]

I would expect a more descriptive exception like AutomatonNotInitializedException or at least an IllegalStateException.