Fix now() sharing global state between tests

src/now.ts

@@ -5,6 +5,15 @@ const tickers: {
     [interval: string]: IResource<number>
 } = {}
 
+export function clearTimers() {
+    for (const key in tickers) {
+        if (tickers.hasOwnProperty(key)) {
+            tickers[key].dispose()
+            delete tickers[key]
+        }
+    }
+}
+
 /**
  * Returns the current date time as epoch number.
  * The date time is read from an observable which is updated automatically after the given interval.
@@ -36,6 +45,7 @@ export function now(interval: number | "frame" = 1000) {
         // See #40
         return Date.now()
     }
+
     if (!tickers[interval]) {
         if (typeof interval === "number") tickers[interval] = createIntervalTicker(interval)
         else tickers[interval] = createAnimationFrameTicker()

test/now.js

@@ -54,3 +54,40 @@ test("now should be up to date when ticker is reactivated, #271", (done) => {
         done()
     }, 200)
 })
+
+describe("given desynchronization is enabled", () => {
+    let actual
+
+    beforeEach(() => {
+        jest.useFakeTimers("modern")
+        jest.setSystemTime(new Date("2015-10-21T07:28:00Z"))
+
+        const someComputed = mobx.computed(() => {
+            const currentTimestamp = utils.now(1000)
+
+            return currentTimestamp > new Date("2015-10-21T07:28:00Z").getTime()
+        })
+
+        mobx.observe(
+            someComputed,
+            (changed) => {
+                actual = changed.newValue
+            },
+            true
+        )
+    })
+
+    afterEach(() => {
+        utils.clearTimers()
+    })
+
+    it("given time passes, works", () => {
+        jest.advanceTimersByTime(1000)
+
+        expect(actual).toBe(true)
+    })
+
+    it("does not share the state from previous test", () => {
+        expect(actual).toBe(false)
+    })
+})