[T] Make Eigen test predicate work with NaNs

Tests/TestTools.h

@@ -79,7 +79,9 @@ struct EigenIsNear
             {
                 auto const diff_comp = diff(r, c);
 
-                if (std::abs(diff_comp) > abstol)
+                if (!(std::abs(diff_comp) <= abstol)
+                    // writing the comparison in this way also works with NaN
+                )
                 {
                     return testing::AssertionFailure()
                            << a_expr << " and " << b_expr << " differ by |"