Fix periodic test module

Add a simple test of periodic_access.

src/source/periodic.rs

@@ -116,3 +116,34 @@ where
         self.input.total_duration()
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use buffer::SamplesBuffer;
+    use std::time::Duration;
+    use source::Source;
+    use std::cell::RefCell;
+
+    #[test]
+    fn stereo_access() {
+        // Stereo, 1Hz audio buffer
+        let inner = SamplesBuffer::new(2, 1, vec![10i16, -10, 10, -10, 20, -20]);
+
+        let cnt = RefCell::new(0);
+
+        let mut source = inner.periodic_access(Duration::from_millis(1000), |_src| {
+            *cnt.borrow_mut() += 1;
+        });
+
+        assert_eq!(*cnt.borrow(), 0);
+        // Always called on first access!
+        assert_eq!(source.next(), Some(10));  assert_eq!(*cnt.borrow(), 1);
+        // Called every 1 second afterwards
+        assert_eq!(source.next(), Some(-10)); assert_eq!(*cnt.borrow(), 1);
+        assert_eq!(source.next(), Some(10));  assert_eq!(*cnt.borrow(), 2);
+        assert_eq!(source.next(), Some(-10)); assert_eq!(*cnt.borrow(), 2);
+        assert_eq!(source.next(), Some(20));  assert_eq!(*cnt.borrow(), 3);
+        assert_eq!(source.next(), Some(-20)); assert_eq!(*cnt.borrow(), 3);
+    }
+}
+