chore: add test comments

spec/operators/catch-spec.ts

@@ -149,6 +149,12 @@ describe('catchError operator', () => {
       const expected = '-1-2-3-5-6-7-     ';
       const unsub = '   ------------!     ';
 
+      // This test is the same as the previous test, but the observable is
+      // manipulated to make it look like an interop observable - an observable
+      // from a foreign library. Interop subscribers are treated differently:
+      // the are wrapped in a safe subscriber. This test ensures that
+      // unsubscriptions are chained all the way to the interop subscriber.
+
       const result = e1.pipe(catchError(() => asInteropObservable(e2)));
 
       expectObservable(result, unsub).toBe(expected);

spec/operators/exhaustMap-spec.ts

@@ -217,6 +217,12 @@ describe('exhaustMap', () => {
 
     const observableLookup = { x: x, y: y, z: z };
 
+    // This test is the same as the previous test, but the observable is
+    // manipulated to make it look like an interop observable - an observable
+    // from a foreign library. Interop subscribers are treated differently:
+    // the are wrapped in a safe subscriber. This test ensures that
+    // unsubscriptions are chained all the way to the interop subscriber.
+
     const result = e1.pipe(
       mergeMap(x => of(x)),
       exhaustMap(value => asInteropObservable(observableLookup[value])),

spec/operators/mergeMap-spec.ts

@@ -273,6 +273,12 @@ describe('mergeMap', () => {
 
     const observableLookup = { x: x, y: y };
 
+    // This test manipulates the observable to make it look like an interop
+    // observable - an observable from a foreign library. Interop subscribers
+    // are treated differently: the are wrapped in a safe subscriber. This
+    // test ensures that unsubscriptions are chained all the way to the
+    // interop subscriber.
+
     const result = e1.pipe(
       mergeMap(x => of(x)),
       mergeMap(value => asInteropObservable(observableLookup[value])),

spec/operators/onErrorResumeNext-spec.ts

@@ -137,6 +137,12 @@ describe('onErrorResumeNext operator', () => {
     const subs =        '^           !';
     const expected =    '--a--b----c--';
 
+    // This test manipulates the observable to make it look like an interop
+    // observable - an observable from a foreign library. Interop subscribers
+    // are treated differently: the are wrapped in a safe subscriber. This
+    // test ensures that unsubscriptions are chained all the way to the
+    // interop subscriber.
+
     expectObservable(source.pipe(onErrorResumeNext(asInteropObservable(next))), subs).toBe(expected);
     expectSubscriptions(next.subscriptions).toBe(nextSubs);
   });

spec/operators/skipUntil-spec.ts

@@ -106,6 +106,12 @@ describe('skipUntil', () => {
     const expected =  ('----------          ');
     const unsub =      '         !          ';
 
+    // This test is the same as the previous test, but the observable is
+    // manipulated to make it look like an interop observable - an observable
+    // from a foreign library. Interop subscribers are treated differently:
+    // the are wrapped in a safe subscriber. This test ensures that
+    // unsubscriptions are chained all the way to the interop subscriber.
+
     const result = e1.pipe(
       mergeMap(x => of(x)),
       skipUntil(asInteropObservable(skip)),

spec/operators/switchMap-spec.ts

@@ -182,6 +182,12 @@ describe('switchMap', () => {
 
     const observableLookup = { x: x, y: y };
 
+    // This test is the same as the previous test, but the observable is
+    // manipulated to make it look like an interop observable - an observable
+    // from a foreign library. Interop subscribers are treated differently:
+    // the are wrapped in a safe subscriber. This test ensures that
+    // unsubscriptions are chained all the way to the interop subscriber.
+
     const result = e1.pipe(
       mergeMap(x => of(x)),
       switchMap(value => asInteropObservable(observableLookup[value])),