test(dtslint): add dtslint test for timer observable static function (#…

…4093) (#4475)

spec-dtslint/observables/timer-spec.ts

@@ -0,0 +1,25 @@
+import { timer, animationFrameScheduler } from 'rxjs';
+
+it('should infer correctly with 1 parameter of number type', () => {
+  const a = timer(1); // $ExpectType Observable<number>
+});
+
+it('should infer correctly with 1 parameter of date type', () => {
+  const a = timer((new Date())); // $ExpectType Observable<number>
+});
+
+it('should not support string parameter', () => {
+  const a = timer('a'); // $ExpectError
+});
+
+it('should infer correctly with 2 parameters', () => {
+  const a = timer(1, 2); // $ExpectType Observable<number>
+});
+
+it('should support scheduler as second parameter', () => {
+  const a = timer(1, animationFrameScheduler); // $ExpectType Observable<number>
+});
+
+it('should support scheduler as third parameter', () => {
+  const a = timer(1, 2, animationFrameScheduler); // $ExpectType Observable<number>
+});