The test failed even without the change "http://" to "//" cause backend.get_embed_code(100, 100) add the iframe. Not sure the separation in two methods is correct.
The iframe has to be rendered. There was a problem with detecting urls without specifing of protocol. Take a look at b8bbd985eeffbeb8cb15decc764fd33a6d06cf72 commit.
The test failed even without the change "http://" to "//" cause backend.get_embed_code(100, 100) add the iframe. Not sure the separation in two methods is correct.