As #595 has shown, builds now fail with Node.js v6.4.0.

As it turns out, the tests fail because of this one test. It tests for yarg's output when a command is supplied that does not have a name. When yargs is about to output that error, it also uses util.inspect to show the content of the supplied command object (reference).

The test output shows that this very output is expected to be slightly different. The original object is:

{ desc: 'A command with no name',
  builder: [Function],
  handler: [Function] }

Interestingly, using util.inspect() on this object generates different outputs on different minors of Node.js v6:

v6.3.1:

'{ desc: \'A command with no name\',\n  builder: [ [Function: Function] ],\n  handler: [ [Function: Function] ] }'

v6.4.0:

'{ desc: \'A command with no name\',\r\n  builder: [ [Function: Function] ],\r\n  handler: [ [Function: Function] ] }'

I'm not sure if this is intended behaviour, so I'll report it on the Node.js repo.