<img width="953" alt="screen shot 2018-03-22 at 4 47 40 pm" src="https://user-images.githubusercontent.com/810438/37785026-037d0788-2df1-11e8-9cbd-5b9e2b2d10db.png">

Caused by this line:

https://github.com/facebook/react/blob/40fa6160534e2bc67b0c43f0b32dcdd1d214068b/scripts/jest/matchers/toWarnDev.js#L52

Calling `jestDiff` with two different strings returns `null`.
'Unexpected warning recorded: ' +
            jestDiff(normalizedMessage, expectedMessages[0]);
        } else {
          errorMessage =
            'Unexpected warning recorded: ' +
            jestDiff([normalizedMessage], expectedMessages);
        }
        
        
        
        unexpectedWarnings.push(new Error(errorMessage));
      };
      
      
      
      const originalMethod = console[consoleMethod];
      
      console[consoleMethod] = consoleSpy;
      try {
        callback();
      } catch (error) {
        caughtError = error;
      } finally {
        
        console[consoleMethod] = originalMethod;
        
        
        if (caughtError) {
          throw caughtError;
        }