MATH-1460: Trigger exception as soon as maximal count is reached.

src/main/java/org/apache/commons/math4/util/IntegerSequence.java

@@ -318,10 +318,11 @@ public class IntegerSequence {
                 throw new NotStrictlyPositiveException(nTimes);
             }
 
+            count += nTimes * increment;
+
             if (!canIncrement(0)) {
                 maxCountCallback.trigger(maximalCount);
             }
-            count += nTimes * increment;
         }
 
         /**
@@ -352,7 +353,7 @@ public class IntegerSequence {
         @Override
         public Integer next() {
             final int value = count;
-            increment();
+            count += increment;
             return value;
         }
 

src/test/java/org/apache/commons/math4/util/IntegerSequenceTest.java

@@ -217,6 +217,33 @@ public class IntegerSequenceTest {
         inc.increment(0);
     }
 
+    @Test
+    public void testIncrementTooManyTimes() {
+        final int start = 0;
+        final int max = 3;
+        final int step = 1;
+
+        for (int i = 1; i <= max + 4; i++) {
+            final IntegerSequence.Incrementor inc
+                = IntegerSequence.Incrementor.create()
+                .withStart(start)
+                .withMaximalCount(max)
+                .withIncrement(step);
+
+            Assert.assertTrue(inc.canIncrement(max - 1));
+            Assert.assertFalse(inc.canIncrement(max));
+
+            try {
+                inc.increment(i);
+            } catch (MaxCountExceededException e) {
+                if (i < max) {
+                    Assert.fail("i=" + i);
+                }
+                // Otherwise, the exception is expected.
+            }
+        }
+    }
+
     @Test(expected=ZeroException.class)
     public void testIncrementZeroStep() {
         final int step = 0;
@@ -269,14 +296,8 @@ public class IntegerSequenceTest {
             .withIncrement(step)
             .withCallback(cb);
 
-        try {
+        Assert.assertTrue(inc.hasNext());
-            // One call must succeed.
+        Assert.assertEquals(start, inc.next().intValue());
-            inc.increment();
+        inc.increment(); // Must fail.
-        } catch (RuntimeException e) {
-            Assert.fail("unexpected exception");
-        }
-
-        // Second call must fail.
-        inc.increment();
     }
 }