test: test sandbox sound driver more rigorously

Consider unexpected values for frequency:

* negative frequency
* zero frequency
* frequency exceeding sampling frequency

As in these cases the sum of the samples is zero also check the count of
the samples.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/sandbox/include/asm/test.h

@@ -188,6 +188,16 @@ int sandbox_get_setup_called(struct udevice *dev);
  */
 int sandbox_get_sound_active(struct udevice *dev);
 
+/**
+ * sandbox_get_sound_count() - Read back the count of the sound data so far
+ *
+ * This data is provided to the sandbox driver by the sound play() method.
+ *
+ * @dev: Device to check
+ * Return: count of audio data
+ */
+int sandbox_get_sound_count(struct udevice *dev);
+
 /**
  * sandbox_get_sound_sum() - Read back the sum of the sound data so far
  *