2.x: fix concatMapEager should accept 0 for prefetch

src/main/java/io/reactivex/Flowable.java

@@ -6789,7 +6789,7 @@ public final <R> Flowable<R> concatMapEager(Function<? super T, ? extends Publis
      * @param mapper the function that maps a sequence of values into a sequence of Publishers that will be
      *               eagerly concatenated
      * @param maxConcurrency the maximum number of concurrent subscribed Publishers
-     * @param prefetch hints about the number of expected source sequence values
+     * @param prefetch hints about the number of expected values from each inner Publisher, must be positive
      * @return the new Publisher instance with the specified concatenation behavior
      * @since 2.0
      */

src/main/java/io/reactivex/Observable.java

@@ -6082,7 +6082,7 @@ public final <R> Observable<R> concatMapEager(Function<? super T, ? extends Obse
      * @param mapper the function that maps a sequence of values into a sequence of ObservableSources that will be
      *               eagerly concatenated
      * @param maxConcurrency the maximum number of concurrent subscribed ObservableSources
-     * @param prefetch hints about the number of expected source sequence values
+     * @param prefetch hints about the number of expected values from each inner ObservableSource, must be positive
      * @return the new ObservableSource instance with the specified concatenation behavior
      * @since 2.0
      */

src/test/java/io/reactivex/internal/operators/flowable/FlowableConcatMapEagerTest.java

@@ -542,12 +542,12 @@ public Flowable<Integer> apply(Integer t) {
     }
 
     @Test(expected = IllegalArgumentException.class)
-    public void testInvalidCapacityHint() {
+    public void testInvalidMaxConcurrent() {
         Flowable.just(1).concatMapEager(toJust, 0, Flowable.bufferSize());
     }
 
     @Test(expected = IllegalArgumentException.class)
-    public void testInvalidMaxConcurrent() {
+    public void testInvalidCapacityHint() {
         Flowable.just(1).concatMapEager(toJust, Flowable.bufferSize(), 0);
     }
 

src/test/java/io/reactivex/internal/operators/observable/ObservableConcatMapEagerTest.java

@@ -509,12 +509,12 @@ public Observable<Integer> apply(Integer t) {
     }
 
     @Test(expected = IllegalArgumentException.class)
-    public void testInvalidCapacityHint() {
+    public void testInvalidMaxConcurrent() {
         Observable.just(1).concatMapEager(toJust, 0, Observable.bufferSize());
     }
 
     @Test(expected = IllegalArgumentException.class)
-    public void testInvalidMaxConcurrent() {
+    public void testInvalidCapacityHint() {
         Observable.just(1).concatMapEager(toJust, Observable.bufferSize(), 0);
     }