1.x: TestSubscriber extra info on assertion failures (ReactiveX#3934)

This PR adds extra information to assertion failure messages on `TestSubscriber` and `TestObserver`, indicating:

  - the listener didn't receive any `onCompleted` calls, which is an indication of hung or skipping operation,
  - there were errors received, indicating a failure in the event generation process.

Previously, if there was something wrong with the sequence, the order and type of assertions were mostly unhelpful: if `assertValues` was first, the lack of values failure could hide a revealing onError call. If the `assertNoErrors()` was first, the error is visible but no way of knowing how far the sequence got.

Now, it is generally okay to use `assertValues` first, which along the difference, will print the lack of completion and the number of exceptions received, plus, the `AssertionError` will have its cause initialized to the actual or composited exception. The message format thus changes:

```
original assertion message with details (0 completions) (+1 error)
...
caused by
...
```

This extra information saved me a lot of time in 2.x and Rsc development.

Note that this change doesn't make the `assertXXX`s also assert for completion or error at all. If the values match, but there is an additional error instead of completion, one has to assert that separately, just like now.

Author: akarnokd

src/main/java/rx/observers/TestObserver.java

@@ -15,12 +15,11 @@
  */
 package rx.observers;
 
-import java.util.ArrayList;
-import java.util.Collections;
-import java.util.List;
+import java.util.*;
 
 import rx.Notification;
 import rx.Observer;
+import rx.exceptions.CompositeException;
 
 /**
  * Observer usable for unit testing to perform assertions, inspect received events or wrap a mocked Observer.
@@ -114,11 +113,12 @@ public List<Object> getEvents() {
      */
     public void assertReceivedOnNext(List<T> items) {
         if (onNextEvents.size() != items.size()) {
-            throw new AssertionError("Number of items does not match. Provided: " + items.size() + "  Actual: " + onNextEvents.size()
+            assertionError("Number of items does not match. Provided: " + items.size() + "  Actual: " + onNextEvents.size()
             + ".\n"
             + "Provided values: " + items
             + "\n"
-            + "Actual values: " + onNextEvents);
+            + "Actual values: " + onNextEvents
+            + "\n");
         }
 
         for (int i = 0; i < items.size(); i++) {
@@ -127,12 +127,12 @@ public void assertReceivedOnNext(List<T> items) {
             if (expected == null) {
                 // check for null equality
                 if (actual != null) {
-                    throw new AssertionError("Value at index: " + i + " expected to be [null] but was: [" + actual + "]");
+                    assertionError("Value at index: " + i + " expected to be [null] but was: [" + actual + "]\n");
                 }
             } else if (!expected.equals(actual)) {
-                throw new AssertionError("Value at index: " + i 
+                assertionError("Value at index: " + i 
                         + " expected to be [" + expected + "] (" + expected.getClass().getSimpleName() 
-                        + ") but was: [" + actual + "] (" + (actual != null ? actual.getClass().getSimpleName() : "null") + ")");
+                        + ") but was: [" + actual + "] (" + (actual != null ? actual.getClass().getSimpleName() : "null") + ")\n");
 
             }
         }
@@ -147,22 +147,64 @@ public void assertReceivedOnNext(List<T> items) {
      */
     public void assertTerminalEvent() {
         if (onErrorEvents.size() > 1) {
-            throw new AssertionError("Too many onError events: " + onErrorEvents.size());
+            assertionError("Too many onError events: " + onErrorEvents.size());
         }
 
         if (onCompletedEvents.size() > 1) {
-            throw new AssertionError("Too many onCompleted events: " + onCompletedEvents.size());
+            assertionError("Too many onCompleted events: " + onCompletedEvents.size());
         }
 
         if (onCompletedEvents.size() == 1 && onErrorEvents.size() == 1) {
-            throw new AssertionError("Received both an onError and onCompleted. Should be one or the other.");
+            assertionError("Received both an onError and onCompleted. Should be one or the other.");
         }
 
         if (onCompletedEvents.size() == 0 && onErrorEvents.size() == 0) {
-            throw new AssertionError("No terminal events received.");
+            assertionError("No terminal events received.");
         }
     }
 
+    /**
+     * Combines an assertion error message with the current completion and error state of this
+     * TestSubscriber, giving more information when some assertXXX check fails.
+     * @param message the message to use for the error
+     */
+    final void assertionError(String message) {
+        StringBuilder b = new StringBuilder(message.length() + 32);
+        
+        b.append(message);
+        
+        
+        b.append(" (");
+        int c = onCompletedEvents.size();
+        b.append(c);
+        b.append(" completion");
+        if (c != 1) {
+            b.append("s");
+        }
+        b.append(")");
+        
+        if (!onErrorEvents.isEmpty()) {
+            int size = onErrorEvents.size();
+            b.append(" (+")
+            .append(size)
+            .append(" error");
+            if (size != 1) {
+                b.append("s");
+            }
+            b.append(")");
+        }
+        
+        AssertionError ae = new AssertionError(b.toString());
+        if (!onErrorEvents.isEmpty()) {
+            if (onErrorEvents.size() == 1) {
+                ae.initCause(onErrorEvents.get(0));
+            } else {
+                ae.initCause(new CompositeException(onErrorEvents));
+            }
+        }
+        throw ae;
+    }
+    
     // do nothing ... including swallowing errors
     private static Observer<Object> INERT = new Observer<Object>() {
 

src/main/java/rx/observers/TestSubscriber.java

@@ -292,7 +292,7 @@ public void assertTerminalEvent() {
      */
     public void assertUnsubscribed() {
         if (!isUnsubscribed()) {
-            throw new AssertionError("Not unsubscribed.");
+            testObserver.assertionError("Not unsubscribed.");
         }
     }
 
@@ -393,10 +393,10 @@ public Thread getLastSeenThread() {
     public void assertCompleted() {
         int s = testObserver.getOnCompletedEvents().size();
         if (s == 0) {
-            throw new AssertionError("Not completed!");
+            testObserver.assertionError("Not completed!");
         } else
         if (s > 1) {
-            throw new AssertionError("Completed multiple times: " + s);
+            testObserver.assertionError("Completed multiple times: " + s);
         }
     }
 
@@ -409,10 +409,10 @@ public void assertCompleted() {
     public void assertNotCompleted() {
         int s = testObserver.getOnCompletedEvents().size();
         if (s == 1) {
-            throw new AssertionError("Completed!");
+            testObserver.assertionError("Completed!");
         } else
         if (s > 1) {
-            throw new AssertionError("Completed multiple times: " + s);
+            testObserver.assertionError("Completed multiple times: " + s);
         }
     }
 
@@ -427,7 +427,7 @@ public void assertNotCompleted() {
     public void assertError(Class<? extends Throwable> clazz) {
         List<Throwable> err = testObserver.getOnErrorEvents();
         if (err.size() == 0) {
-            throw new AssertionError("No errors");
+            testObserver.assertionError("No errors");
         } else
         if (err.size() > 1) {
             AssertionError ae = new AssertionError("Multiple errors: " + err.size());
@@ -452,7 +452,7 @@ public void assertError(Class<? extends Throwable> clazz) {
     public void assertError(Throwable throwable) {
         List<Throwable> err = testObserver.getOnErrorEvents();
         if (err.size() == 0) {
-            throw new AssertionError("No errors");
+            testObserver.assertionError("No errors");
         } else
         if (err.size() > 1) {
             AssertionError ae = new AssertionError("Multiple errors: " + err.size());
@@ -477,7 +477,7 @@ public void assertNoTerminalEvent() {
         int s = testObserver.getOnCompletedEvents().size();
         if (err.size() > 0 || s > 0) {
             if (err.isEmpty()) {
-                throw new AssertionError("Found " + err.size() + " errors and " + s + " completion events instead of none");
+                testObserver.assertionError("Found " + err.size() + " errors and " + s + " completion events instead of none");
             } else
             if (err.size() == 1) {
                 AssertionError ae = new AssertionError("Found " + err.size() + " errors and " + s + " completion events instead of none");
@@ -500,7 +500,7 @@ public void assertNoTerminalEvent() {
     public void assertNoValues() {
         int s = testObserver.getOnNextEvents().size();
         if (s > 0) {
-            throw new AssertionError("No onNext events expected yet some received: " + s);
+            testObserver.assertionError("No onNext events expected yet some received: " + s);
         }
     }
 
@@ -514,7 +514,7 @@ public void assertNoValues() {
     public void assertValueCount(int count) {
         int s = testObserver.getOnNextEvents().size();
         if (s != count) {
-            throw new AssertionError("Number of onNext events differ; expected: " + count + ", actual: " + s);
+            testObserver.assertionError("Number of onNext events differ; expected: " + count + ", actual: " + s);
         }
     }
 

src/test/java/rx/observers/TestSubscriberTest.java

@@ -18,16 +18,18 @@
 import static org.junit.Assert.*;
 import static org.mockito.Mockito.*;
 
-import java.util.Arrays;
+import java.util.*;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.junit.*;
 import org.junit.rules.ExpectedException;
 import org.mockito.InOrder;
 
-import rx.*;
+import rx.Observable;
+import rx.Observer;
 import rx.Scheduler.Worker;
+import rx.Subscriber;
 import rx.exceptions.*;
 import rx.functions.Action0;
 import rx.schedulers.Schedulers;
@@ -610,9 +612,105 @@ public void assertValuesShouldThrowIfNumberOfItemsDoesNotMatch() {
         } catch (AssertionError expected) {
             assertEquals("Number of items does not match. Provided: 2  Actual: 3.\n" +
                     "Provided values: [1, 2]\n" +
-                    "Actual values: [a, b, c]",
+                    "Actual values: [a, b, c]\n (0 completions)",
                     expected.getMessage()
             );
         }
     }
+    
+    @Test
+    public void assertionFailureGivesActiveDetails() {
+        TestSubscriber<String> ts = new TestSubscriber<String>();
+
+        ts.onNext("a");
+        ts.onNext("b");
+        ts.onNext("c");
+        ts.onError(new TestException("forced failure"));
+
+        try {
+            ts.assertValues("1", "2");
+            fail();
+        } catch (AssertionError expected) {
+            assertEquals("Number of items does not match. Provided: 2  Actual: 3.\n" +
+                    "Provided values: [1, 2]\n" +
+                    "Actual values: [a, b, c]\n (0 completions) (+1 error)",
+                    expected.getMessage()
+            );
+            Throwable ex = expected.getCause();
+            assertEquals(TestException.class, ex.getClass());
+            assertEquals("forced failure", ex.getMessage());
+        }
+    }
+    
+    @Test
+    public void assertionFailureShowsMultipleErrors() {
+        TestSubscriber<String> ts = new TestSubscriber<String>();
+
+        ts.onNext("a");
+        ts.onNext("b");
+        ts.onNext("c");
+        ts.onError(new TestException("forced failure"));
+        ts.onError(new TestException("forced failure 2"));
+
+        try {
+            ts.assertValues("1", "2");
+            fail();
+        } catch (AssertionError expected) {
+            assertEquals("Number of items does not match. Provided: 2  Actual: 3.\n" +
+                    "Provided values: [1, 2]\n" +
+                    "Actual values: [a, b, c]\n (0 completions) (+2 errors)",
+                    expected.getMessage()
+            );
+            Throwable ex = expected.getCause();
+            assertEquals(CompositeException.class, ex.getClass());
+            List<Throwable> list = ((CompositeException)ex).getExceptions();
+            assertEquals(2, list.size());
+            assertEquals("forced failure", list.get(0).getMessage());
+            assertEquals("forced failure 2", list.get(1).getMessage());
+        }
+    }
+
+    @Test
+    public void assertionFailureShowsCompletion() {
+        TestSubscriber<String> ts = new TestSubscriber<String>();
+
+        ts.onNext("a");
+        ts.onNext("b");
+        ts.onNext("c");
+        ts.onCompleted();
+
+        try {
+            ts.assertValues("1", "2");
+            fail();
+        } catch (AssertionError expected) {
+            assertEquals("Number of items does not match. Provided: 2  Actual: 3.\n" +
+                    "Provided values: [1, 2]\n" +
+                    "Actual values: [a, b, c]\n (1 completion)",
+                    expected.getMessage()
+            );
+        }
+    }
+
+    @Test
+    public void assertionFailureShowsMultipleCompletions() {
+        TestSubscriber<String> ts = new TestSubscriber<String>();
+
+        ts.onNext("a");
+        ts.onNext("b");
+        ts.onNext("c");
+        ts.onCompleted();
+        ts.onCompleted();
+
+        try {
+            ts.assertValues("1", "2");
+            fail();
+        } catch (AssertionError expected) {
+            assertEquals("Number of items does not match. Provided: 2  Actual: 3.\n" +
+                    "Provided values: [1, 2]\n" +
+                    "Actual values: [a, b, c]\n (2 completions)",
+                    expected.getMessage()
+            );
+        }
+    }
+
 }