feat: Add FeatureValue.variants[].priority sorting tests (#28)

Co-authored-by: Zaimwa9 <[email protected]>

Author: khvn26

test_cases/test_multivariate__option_a_stronger_priority__expected_flags.jsonc

@@ -0,0 +1,51 @@
+{
+  // Given: A multivariate feature with two variants of equal weight, where option_b has a stronger priority (lower priority number)
+  //        and an identity resulting in 49.27% percentage allocation
+  // When: Evaluating the feature for the given identity
+  // Then: The variant with stronger priority (option_a) should be selected as the feature value
+  "$schema": "https://raw.githubusercontent.com/Flagsmith/engine-test-data/refs/tags/v2.0.0/schema.json",
+  "context": {
+    "environment": {
+      "key": "test_env",
+      "name": "Test Environment"
+    },
+    "identity": {
+      "identifier": "0cfd0d72-4de4-4ed7-9cfb-d80dc3dacead",
+      "key": "32103813"
+    },
+    "features": {
+      "multivariate_feature": {
+        "enabled": true,
+        "feature_key": "15062",
+        "key": "78986",
+        "name": "multivariate_feature",
+        "value": "foo",
+        "variants": [
+          {
+            "value": "option_a",
+            "weight": 50,
+            "priority": 10
+          },
+          {
+            "value": "option_b",
+            "weight": 50,
+            "priority": 20
+          }
+        ]
+      }
+    },
+    "segments": {}
+  },
+  "result": {
+    "flags": {
+      "multivariate_feature": {
+        "enabled": true,
+        "feature_key": "15062",
+        "name": "multivariate_feature",
+        "reason": "SPLIT; weight=50",
+        "value": "option_a"
+      }
+    },
+    "segments": []
+  }
+}

test_cases/test_multivariate__option_b_stronger_priority__expected_flags.jsonc

@@ -0,0 +1,51 @@
+{
+  // Given: A multivariate feature with two variants of equal weight, where option_b has a stronger priority (lower priority number)
+  //        and an identity resulting in 49.27% percentage allocation
+  // When: Evaluating the feature for the given identity
+  // Then: The variant with stronger priority (option_b) should be selected as the feature value
+  "$schema": "https://raw.githubusercontent.com/Flagsmith/engine-test-data/refs/tags/v2.0.0/schema.json",
+  "context": {
+    "environment": {
+      "key": "test_env",
+      "name": "Test Environment"
+    },
+    "identity": {
+      "identifier": "0cfd0d72-4de4-4ed7-9cfb-d80dc3dacead",
+      "key": "32103813"
+    },
+    "features": {
+      "multivariate_feature": {
+        "enabled": true,
+        "feature_key": "15062",
+        "key": "78986",
+        "name": "multivariate_feature",
+        "value": "foo",
+        "variants": [
+          {
+            "value": "option_a",
+            "weight": 50,
+            "priority": 20
+          },
+          {
+            "value": "option_b",
+            "weight": 50,
+            "priority": 10
+          }
+        ]
+      }
+    },
+    "segments": {}
+  },
+  "result": {
+    "flags": {
+      "multivariate_feature": {
+        "enabled": true,
+        "feature_key": "15062",
+        "name": "multivariate_feature",
+        "reason": "SPLIT; weight=50",
+        "value": "option_b"
+      }
+    },
+    "segments": []
+  }
+}