In a fresh installation of MediaWiki as of d364241 on an older VM running Lubuntu and PHP 5.5.9 I got hundres of tests erroring out (see P6019) with a good deal of them having to do with cURL.
Obviously, installed php5-curl resolved the issue. Perhaps similar to https://gerrit.wikimedia.org/r/#/c/378420/ we should add a depency check for HttpTest? Adding @matmarex to open.