Apply suggestion from @ericspod

Signed-off-by: Eric Kerfoot <17726042+ericspod@users.noreply.github.com>

Author: ericspod

tests/metrics/test_ssim_metric.py

@@ -32,7 +32,7 @@ def test_2d_gaussian(self):
         metric(preds, target)
         result = metric.aggregate()
         expected_value = 0.045415
-        self.assertTrue(expected_value - result.item() < 0.000001)
+        self.assertTrue(abs(expected_value - result.item()) < 0.000001)
 
     def test_2d_uniform(self):
         set_determinism(0)