Assert calculated test task names are distinct between each other for the same test suite

[lacasseio]

I don't think we make this assertion which we could have something like:

myTestSuite {
    testingStrategies = [new MyCustomStrategyNamed('foo'), new MyOtherCustomStrategyNamed('foo')]
}

Assuming the name passed to the constructor is the Named of the strategy, we would calculate myTestSuiteFoo for both Test tasks. Note that using MyCustomStrategyNamed or MyOtherCustomStrategyNamed twice with the same constructor argument would in theory be a no-op as testingStrategies is a SetProperty and both strategy implementations should implement proper hash code and equals.

We don't believe it's an actual bug but it may become one when solving #70