Pharmacy chain Walgreens has filed a breach of contract suit against failed blood-testing startup Theranos. The suit, reportedly for $140 million, follows the termination of the companies' business relationship in June. Walgreens had previously been Theranos's largest partner. Theranos claimed to be able to perform medical tests with just a few drops of blood. But after series of investigations raised serious questions on the legitimacy of Theranos's core business claims, the company began a death spiral, closing its lab operations in October.