test(dtslint): add switchMapTo

spec-dtslint/operators/switchMapTo-spec.ts

@@ -0,0 +1,47 @@
+import { of } from 'rxjs';
+import { switchMapTo } from 'rxjs/operators';
+
+it('should infer correctly', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(of('foo'))); // $ExpectType Observable<string>
+});
+
+it('should infer correctly with multiple types', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(of('foo', 4))); // $ExpectType Observable<string | number>
+});
+
+it('should infer correctly with an array', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo([4, 5, 6])); // $ExpectType Observable<number>
+});
+
+it('should infer correctly with a Promise', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(new Promise<string>(() => {}))); // $ExpectType Observable<string>
+});
+
+it('should infer correctly by using the resultSelector first parameter', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(of('foo'), a => a)); // $ExpectType Observable<number>
+});
+
+it('should infer correctly by using the resultSelector second parameter', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(of('foo'), (a, b) => b)); // $ExpectType Observable<string>
+});
+
+it('should support a resultSelector that takes an inner index', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(of('foo'), (a, b, innnerIndex) => a)); // $ExpectType Observable<number>
+});
+
+it('should support a resultSelector that takes an inner and outer index', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(of('foo'), (a, b, innnerIndex, outerIndex) => a)); // $ExpectType Observable<number>
+});
+
+it('should support an undefined resultSelector', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(of('foo'), undefined)); // $ExpectType Observable<string>
+});
+
+it('should enforce types', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo()); // $ExpectError
+});
+
+it('should enforce the return type', () => {
+  const o = of(1, 2, 3).pipe(switchMapTo(p => p)); // $ExpectError
+  const p = of(1, 2, 3).pipe(switchMapTo(4)); // $ExpectError
+});