[Test][FP] TaintTransform on Args

[the-storm]

Summary

Minimal test showing a FP on Transform for the following piece of code

void test_fp {
   Object source = Origin.source();
    transformT1OnArg(source);
    Origin.sink(source);
}

Expected to see only one flow which is Source -> T1 -> Sink
Actual: 2 flows

• Source -> Sink <-- This flow is FP
• Source -> T1 -> Sink

[the-storm]

@arthaud This flow is unexpected

[arthaud]

Discussed this offline.
This is the expected outcome and not a false positive, since propagations are applied with "weak" updates by default,
which means the resulting taint after a method call is the original taint joined with the effect of propagations.
In this example, that means we end up with 2 flows: one with the transform and one without the transform.
You could use the mode strong-write-on-propagation on transformT1OnArg to avoid this, but be careful as this could lead to false negatives.