test: add failing invalid ObservableInput tests

spec/operators/concatMap-spec.ts

@@ -691,4 +691,17 @@ describe('Observable.prototype.concatMap', () => {
         done(new Error('Subscriber complete handler not supposed to be called.'));
       });
   });
+
+  it('should report invalid observable inputs via error notifications', () => {
+    const e1 =    hot('--1|');
+    const e1subs =    '^ !';
+    const expected =  '--#';
+
+    const result = e1.pipe(concatMap(() => null as any));
+
+    expectObservable(result).toBe(expected, null, new TypeError(
+      "You provided 'null' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable."
+    ));
+    expectSubscriptions(e1.subscriptions).toBe(e1subs);
+  });
 });

spec/operators/exhaustMap-spec.ts

@@ -434,4 +434,17 @@ describe('exhaustMap', () => {
     expectSubscriptions(x.subscriptions).toBe(xsubs);
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
+
+  it('should report invalid observable inputs via error notifications', () => {
+    const e1 =    hot('--1|');
+    const e1subs =    '^ !';
+    const expected =  '--#';
+
+    const result = e1.pipe(exhaustMap(() => null as any));
+
+    expectObservable(result).toBe(expected, null, new TypeError(
+      "You provided 'null' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable."
+    ));
+    expectSubscriptions(e1.subscriptions).toBe(e1subs);
+  });
 });

spec/operators/mergeMap-spec.ts

@@ -852,4 +852,17 @@ describe('mergeMap', () => {
       expectObservable(result).toBe(expected, undefined, noXError);
     });
   });
+
+  it('should report invalid observable inputs via error notifications', () => {
+    const e1 =    hot('--1|');
+    const e1subs =    '^ !';
+    const expected =  '--#';
+
+    const result = e1.pipe(mergeMap(() => null as any));
+
+    expectObservable(result).toBe(expected, null, new TypeError(
+      "You provided 'null' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable."
+    ));
+    expectSubscriptions(e1.subscriptions).toBe(e1subs);
+  });
 });

spec/operators/switchMap-spec.ts

@@ -444,4 +444,17 @@ describe('switchMap', () => {
     expectSubscriptions(x.subscriptions).toBe(xsubs);
     expectSubscriptions(e1.subscriptions).toBe(e1subs);
   });
+
+  it('should report invalid observable inputs via error notifications', () => {
+    const e1 =    hot('--1|');
+    const e1subs =    '^ !';
+    const expected =  '--#';
+
+    const result = e1.pipe(switchMap(() => null as any));
+
+    expectObservable(result).toBe(expected, null, new TypeError(
+      "You provided 'null' where a stream was expected. You can provide an Observable, Promise, Array, or Iterable."
+    ));
+    expectSubscriptions(e1.subscriptions).toBe(e1subs);
+  });
 });