In January 2017, a screenshot of a tweet purportedly sent by President Donald Trump (pledging "mandatory drug testing" for recipients of public assistance) circulated on social media. The text of the suspiciously undated tweet read "Drug test will be mandatory before receiving anything the government has to offer! We have to clean up these streets!":
The San Fran crash was totally the pilot's fault - may be too late for drug testing, RIDICULOUS!
— Donald J. Trump (@realDonaldTrump) July 9, 2013
Given the lack of standard Twitter formatting, and the lack of any attendant news coverage about it (despite all the attention paid to Trump's Twitter feed by the news media), it's safe to say this tweet was fabricated and does not represent any statements made by President Trump via Twitter in January 2017.