[FLINK-1522][FLINK-1576] Updated LabelPropagationExample and test

[balidani]

Hi!

I converted the Label Propagation example to the conventional format, where the main program takes (optional) arguments. I added a test case as well.

Cheers!

[vasia]

Thanks for this PR @balidani!

In my opinion, we could extend the test case a bit.
It's quite hard to check correctness for this kind of algorithms, but we can still test that the behavior is as expected, inside a single iteration.
More specifically, I would test the following scenarios:

• initialize a graph where it is trivial to find the most frequently occurring label for each vertex. Test that every vertex indeed adopts the correct label in the next iteration.
• initialize a graph where for one vertex, there are two labels with the same frequency. Test that ties are broken by adopting the label with the highest value.
• when no vertex changes label, the algorithm terminates.

[balidani]

Hi @vasia!

Thanks for the ideas! I tried to add more test cases that reflect them.
However, I'm not sure about the last bullet-point. Do you think my last test case matches this?

Cheers!

[vasia]

Hi @balidani! You're right, there is no way to check this without modifying the library method. You can ignore my last bullet point for now :)