Update.

test/timer/immediate.wren

@@ -0,0 +1,15 @@
+// retoor <retoor@molodetz.nl>
+
+import "timer" for Timer
+
+var called = false
+
+Timer.immediate {
+    called = true
+}
+
+System.print(called) // expect: false
+
+Timer.sleep(1)
+
+System.print(called) // expect: true

test/timer/interval.wren

@@ -0,0 +1,20 @@
+// retoor <retoor@molodetz.nl>
+
+import "timer" for Timer, TimerHandle
+
+var count = 0
+var handle = Timer.interval(1) {
+    count = count + 1
+}
+
+System.print(handle is TimerHandle) // expect: true
+System.print(handle.isActive) // expect: true
+
+Timer.sleep(100)
+handle.stop()
+
+System.print(count > 0) // expect: true
+System.print(handle.isActive) // expect: false
+
+
+System.print(count) // nontest

test/timer/sleep.wren

@@ -0,0 +1,6 @@
+// retoor <retoor@molodetz.nl>
+
+import "timer" for Timer
+
+Timer.sleep(10)
+System.print("after sleep") // expect: after sleep