test(dtslint): add dtslint test for forkjoin obsrevable (#4093) (#4414)

* test(dtslint): add dtslint test for forkjoin obsrevable (#4093)

* chore(forkJoin): update dtslint with TODOs for what needs fixed

spec-dtslint/observables/forkJoin-spec.ts

@@ -0,0 +1,94 @@
+import { of, forkJoin } from 'rxjs';
+
+it('should infer correctly with 1 parameter', () => {
+  const a = of(1, 2, 3);
+  const res = forkJoin(a); // $ExpectType Observable<number[]>
+});
+
+it('should infer correctly with 2 parameters', () => {
+  const a = of(1, 2, 3);
+  const b = of('a', 'b', 'c');
+  const res = forkJoin(a, b); // $ExpectType Observable<[number, string]>
+});
+
+it('should infer correctly with 3 parameters', () => {
+  const a = of(1, 2, 3);
+  const b = of('a', 'b', 'c');
+  const c = of(1, 2, 3);
+  const res = forkJoin(a, b, c); // $ExpectType Observable<[number, string, number]>
+});
+
+it('should infer correctly with 4 parameters', () => {
+  const a = of(1, 2, 3);
+  const b = of('a', 'b', 'c');
+  const c = of(1, 2, 3);
+  const d = of(1, 2, 3);
+  const res = forkJoin(a, b, c, d); // $ExpectType Observable<[number, string, number, number]>
+});
+
+it('should infer correctly with 5 parameters', () => {
+  const a = of(1, 2, 3);
+  const b = of('a', 'b', 'c');
+  const c = of(1, 2, 3);
+  const d = of(1, 2, 3);
+  const e = of(1, 2, 3);
+  const res = forkJoin(a, b, c, d, e); // $ExpectType Observable<[number, string, number, number, number]>
+});
+
+it('should infer correctly with 6 parameters', () => {
+  const a = of(1, 2, 3);
+  const b = of('a', 'b', 'c');
+  const c = of(1, 2, 3);
+  const d = of(1, 2, 3);
+  const e = of(1, 2, 3);
+  const f = of(1, 2, 3);
+  const res = forkJoin(a, b, c, d, e, f); // $ExpectType Observable<[number, string, number, number, number, number]>
+});
+
+// TODO(benlesh): this needs to be fixed as well
+// it('should infer of type any for more than 6 parameters', () => {
+//   const a = of(1, 2, 3);
+//   const b = of('a', 'b', 'c');
+//   const c = of(1, 2, 3);
+//   const d = of(1, 2, 3);
+//   const e = of(1, 2, 3);
+//   const f = of(1, 2, 3);
+//   const g = of(1, 2, 3);
+//   const res = forkJoin(a, b, c, d, e, f, g); // $ExpectType Observable<{}>
+// });
+
+it('should infer correctly for array of 1 observable', () => {
+  const a = [of(1, 2, 3)];
+  const res = forkJoin(a); // $ExpectType Observable<number[]>
+});
+
+// TODO(benlesh): We need to fix forkJoin so these pass
+// it('should infer correctly for array of 2 observables', () => {
+//   const a = [of(1, 2, 3), of('a', 'b', 'c')];
+//   const res = forkJoin(a); // $ExpectType Observable<[number, string]>
+// });
+
+// it('should infer correctly for array of 3 observables', () => {
+//   const a = [of(1, 2, 3), of('a', 'b', 'c'), of(true, true, false)];
+//   const res = forkJoin(a); // $ExpectType Observable<[number, string, boolean]>
+// });
+
+// it('should infer correctly for array of 4 observables', () => {
+//   const a = [of(1, 2, 3), of('a', 'b', 'c'), of(1, 2, 3), of(1, 2, 3)];
+//   const res = forkJoin(a); // $ExpectType Observable<[number, string, number, number]>
+// });
+
+// it('should infer correctly for array of 5 observables', () => {
+//   const a = [of(1, 2, 3), of('a', 'b', 'c'), of(1, 2, 3), of(1, 2, 3), of(1, 2, 3)];
+//   const res = forkJoin(a); // $ExpectType Observable<[number, string, number, number, number]>
+// });
+
+// it('should infer correctly for array of 6 observables', () => {
+//   const a = [of(1, 2, 3), of('a', 'b', 'c'), of(1, 2, 3), of(1, 2, 3), of(1, 2, 3), of(1, 2, 3)];
+//   const res = forkJoin(a); // $ExpectType Observable<[number, string, number, number, number, number]>
+// });
+
+// it('should force user cast for array of 6+ observables', () => {
+//   const a = [of(1, 2, 3), of('a', 'b', 'c'), of(1, 2, 3), of(1, 2, 3), of(1, 2, 3), of(1, 2, 3), of(1, 2, 3)];
+//   const res = forkJoin(a); // $ExpectType Observable<{}>
+// });