+1 failing test: clock signal using setInterval, clearInterval and precise time fcn
+1 test pass: clock signal using setInterval, clearInterval...
+3 passing tests: clock with different timing values
+1 test pass: clearInterval should be called if clock stopped
+5 failing tests: clock should call clearInterval with the same handlers returned by createInterval when stopped
+5 test pass: clock should call clearInterval with the same handlers returned by createInterval when stopped