add another unittest for new mean/median/quantile# masking conditions

there was none for the determinist side

tests/test_determinist.cpp

@@ -217,7 +217,7 @@ TEST(DeterministTests, TestMaskingConditions)
     // generate dummy empty masks required to access next optional argument
     xt::xtensor<bool, 2> masks;
 
-    // conditions on streamflow ________________________________________________
+    // conditions on streamflow values _________________________________________
 
     // compute scores using masking conditions on streamflow to subset whole record
     xt::xtensor<std::array<char, 32>, 2> q_conditions ={
@@ -248,6 +248,39 @@ TEST(DeterministTests, TestMaskingConditions)
         ) << "Failure for (" << metrics[m] << ")";
     }
 
+    // conditions on streamflow statistics _____________________________________
+
+    // compute scores using masking conditions on streamflow to subset whole record
+    xt::xtensor<std::array<char, 32>, 2> q_conditions_ ={
+            {{"q_obs{>=mean}"}}
+    };
+
+    double mean = xt::mean(observed, {1})();
+
+    std::vector<xt::xarray<double>> metrics_q_conditioned_ =
+            evalhyd::evald<2>(
+                    observed, predicted, metrics,
+                    "none", 1, -9, masks, q_conditions_
+            );
+
+    // compute scores using "NaN-ed" time indices where conditions on streamflow met
+    std::vector<xt::xarray<double>> metrics_q_preconditioned_ =
+            evalhyd::evald<2>(
+                    xt::where(observed >= mean, observed, NAN),
+                    predicted,
+                    metrics
+            );
+
+    // check results are identical
+    for (int m = 0; m < metrics.size(); m++)
+    {
+        EXPECT_TRUE(
+                xt::allclose(
+                        metrics_q_conditioned[m], metrics_q_preconditioned[m]
+                )
+        ) << "Failure for (" << metrics[m] << ")";
+    }
+
     // conditions on temporal indices __________________________________________
 
     // compute scores using masking conditions on time indices to subset whole record