What is the test for establishing a hostile work environment?

"To establish a prima facie case of hostile work environment, the plaintiff must show that the discriminatory harassment was sufficiently severe or pervasive to alter the conditions of the victim's employment and create an abusive working environment, and that a specific basis exists for imputing the objectionable conduct to the employer." Tolbert v. Smith, 790 F.3d 427, 439 (2d Cir. 2015) (internal quotation marks omitted). "Isolated acts, unless very serious, do not meet the threshold of severity or pervasiveness." Id. (internal quotation marks omitted). "It is axiomatic that the plaintiff also must show that the hostile conduct occurred because of a protected characteristic." Id.