2.x: Add assertValuesOnly to BaseTestConsumer. (#5568)

* 2.x: Add assertValuesOnly to BaseTestConsumer.

* Address comments.

Author: vanniktech

src/main/java/io/reactivex/observers/BaseTestConsumer.java

@@ -522,6 +522,21 @@ public final U assertValues(T... values) {
         return (U)this;
     }
 
+    /**
+     * Assert that the TestObserver/TestSubscriber received only the specified values in the specified order without terminating.
+     * @param values the values expected
+     * @return this;
+     * @since 2.1.4
+     */
+    @SuppressWarnings("unchecked")
+    @Experimental
+    public final U assertValuesOnly(T... values) {
+        return assertSubscribed()
+                .assertValues(values)
+                .assertNoErrors()
+                .assertNotComplete();
+    }
+
     /**
      * Assert that the TestObserver/TestSubscriber received only the specified values in any order.
      * <p>This helps asserting when the order of the values is not guaranteed, i.e., when merging

src/test/java/io/reactivex/observers/TestObserverTest.java

@@ -1439,4 +1439,66 @@ public void withTag() {
             assertTrue(ex.toString(), ex.toString().contains("testing with item=2"));
         }
     }
+
+    @Test
+    public void assertValuesOnly() {
+        TestObserver<Integer> to = TestObserver.create();
+        to.onSubscribe(Disposables.empty());
+        to.assertValuesOnly();
+
+        to.onNext(5);
+        to.assertValuesOnly(5);
+
+        to.onNext(-1);
+        to.assertValuesOnly(5, -1);
+    }
+
+    @Test
+    public void assertValuesOnlyThrowsOnUnexpectedValue() {
+        TestObserver<Integer> to = TestObserver.create();
+        to.onSubscribe(Disposables.empty());
+        to.assertValuesOnly();
+
+        to.onNext(5);
+        to.assertValuesOnly(5);
+
+        to.onNext(-1);
+
+        try {
+            to.assertValuesOnly(5);
+            fail();
+        } catch (AssertionError ex) {
+            // expected
+        }
+    }
+
+    @Test
+    public void assertValuesOnlyThrowsWhenCompleted() {
+        TestObserver<Integer> to = TestObserver.create();
+        to.onSubscribe(Disposables.empty());
+
+        to.onComplete();
+
+        try {
+            to.assertValuesOnly();
+            fail();
+        } catch (AssertionError ex) {
+            // expected
+        }
+    }
+
+    @Test
+    public void assertValuesOnlyThrowsWhenErrored() {
+        TestObserver<Integer> to = TestObserver.create();
+        to.onSubscribe(Disposables.empty());
+
+        to.onError(new TestException());
+
+        try {
+            to.assertValuesOnly();
+            fail();
+        } catch (AssertionError ex) {
+            // expected
+        }
+    }
 }

src/test/java/io/reactivex/subscribers/TestSubscriberTest.java

@@ -1997,4 +1997,66 @@ public void waitStrategyRuns() {
             ws.run();
         }
     }
+
+    @Test
+    public void assertValuesOnly() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+        ts.onSubscribe(new BooleanSubscription());
+        ts.assertValuesOnly();
+
+        ts.onNext(5);
+        ts.assertValuesOnly(5);
+
+        ts.onNext(-1);
+        ts.assertValuesOnly(5, -1);
+    }
+
+    @Test
+    public void assertValuesOnlyThrowsOnUnexpectedValue() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+        ts.onSubscribe(new BooleanSubscription());
+        ts.assertValuesOnly();
+
+        ts.onNext(5);
+        ts.assertValuesOnly(5);
+
+        ts.onNext(-1);
+
+        try {
+            ts.assertValuesOnly(5);
+            fail();
+        } catch (AssertionError ex) {
+            // expected
+        }
+    }
+
+    @Test
+    public void assertValuesOnlyThrowsWhenCompleted() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+        ts.onSubscribe(new BooleanSubscription());
+
+        ts.onComplete();
+
+        try {
+            ts.assertValuesOnly();
+            fail();
+        } catch (AssertionError ex) {
+            // expected
+        }
+    }
+
+    @Test
+    public void assertValuesOnlyThrowsWhenErrored() {
+        TestSubscriber<Integer> ts = TestSubscriber.create();
+        ts.onSubscribe(new BooleanSubscription());
+
+        ts.onError(new TestException());
+
+        try {
+            ts.assertValuesOnly();
+            fail();
+        } catch (AssertionError ex) {
+            // expected
+        }
+    }
 }