Is there any npm library containing only assertions?

I've wrote very-very simple testing engine for my application, that totally satisfies me.

However, currently test passing logic is as simple as:

return foo === bar 

or

return foo.length === 3

Therefore, if test fails, I have to manually console.log() those variables, in order to analyze their values. I do not want to install full testing library like Mocha, instead I would like to only install assertions library, so I could use assertEquals(), assertTrue() etc.