diff --git a/src/dotnet/QuantEngine.Core.Tests/BffApiTests.cs b/src/dotnet/QuantEngine.Core.Tests/BffApiTests.cs
new file mode 100644
index 00000000..69b15bee
--- /dev/null
+++ b/src/dotnet/QuantEngine.Core.Tests/BffApiTests.cs
@@ -0,0 +1,62 @@
+using System;
+using System.IO;
+using System.Text;
+using System.Text.Json;
+using Xunit;
+
+namespace QuantEngine.Core.Tests
+{
+    public class BffApiTests
+    {
+        [Fact]
+        public void UpdateFactorThreshold_ValidJson_ParsesCorrectly()
+        {
+            // Arrange
+            var jsonString = "{\"momentum_lookback\": 20, \"volatility_cap\": 0.05}";
+
+            // Act
+            using var doc = JsonDocument.Parse(jsonString);
+            var root = doc.RootElement;
+            var lookback = root.GetProperty("momentum_lookback").GetInt32();
+            var cap = root.GetProperty("volatility_cap").GetDouble();
+
+            // Assert
+            Assert.Equal(20, lookback);
+            Assert.Equal(0.05, cap);
+        }
+
+        [Fact]
+        public void ExportStreamingFactorOlap_WriteCsvRow_MatchesExpectedFormat()
+        {
+            // Arrange
+            var sb = new StringBuilder();
+            var headers = new[] { "ticker", "as_of_date", "close_price", "nav_price" };
+            sb.AppendLine(string.Join(",", headers));
+
+            var row = new object[] { "123456", "2026-07-25", 50000, 49800 };
+            sb.AppendLine(string.Join(",", row));
+
+            // Act
+            var output = sb.ToString();
+
+            // Assert
+            Assert.Contains("ticker,as_of_date,close_price,nav_price", output);
+            Assert.Contains("123456,2026-07-25,50000,49800", output);
+        }
+
+        [Fact]
+        public void BulkInsertMarketExcel_EmptyCellValidation_DetectsNull()
+        {
+            // Arrange
+            string? ticker = null;
+            double? price = null;
+
+
+            // Act
+            bool isInvalid = string.IsNullOrEmpty(ticker) || !price.HasValue;
+
+            // Assert
+            Assert.True(isInvalid);
+        }
+    }
+}