Assertions

Is there a way to use Java assertions?

Using a Python3 kernel and the line:

assert(1==2)

an AssertionError is returned:

AssertionErrorTraceback (most recent call last)
<ipython-input-2-000000000000> in <module>()
----> 1 assert(1==2);

AssertionError:

Using the IJava kernel and the same line, there is no return value or exception displayed.

[SpencerPark]

Assertions in java are a bit different, there is the assert keyword but it is disabled by default. To enable it the -ea flag must be passed in the jvm arguments. In the IJava kernel this can be done by editing the kernel.json and adding the -ea flag to the argv list but this makes your notebooks less reproducible as users would require the same setup.

What I would recommend is use a library like junit assertions which are common in java unit testing and easily included with the maven magic.

Run a cell with the following to include all of the assert methods from junit to the static space in your notebook:

%maven junit:junit:4.12
import static org.junit.Assert.*;

Use the assertion methods like the following:

assertTrue("Assertion message", 1 == 1);
assertTrue(1 == 2);

which is the same as the following pure java code if -ea is enabled:

assert 1 == 1: "Assertion message";
assert 1 == 2;

[hkarl]

Thanks for following up! Current preliminary testing seems to indicate it works. It will get its main workout when we run >400 students and their homeworks through it in December 😃 - we will keep you posted.