diff --git a/tests/ScadaLink.CentralUI.Tests/DataConnectionFormTests.cs b/tests/ScadaLink.CentralUI.Tests/DataConnectionFormTests.cs
new file mode 100644
index 0000000..5e13757
--- /dev/null
+++ b/tests/ScadaLink.CentralUI.Tests/DataConnectionFormTests.cs
@@ -0,0 +1,100 @@
+using System.Security.Claims;
+using System.Text.Json;
+using Bunit;
+using Microsoft.AspNetCore.Components.Authorization;
+using Microsoft.Extensions.DependencyInjection;
+using NSubstitute;
+using ScadaLink.Commons.Entities.Sites;
+using ScadaLink.Commons.Interfaces.Repositories;
+using DataConnectionForm = ScadaLink.CentralUI.Components.Pages.Admin.DataConnectionForm;
+
+namespace ScadaLink.CentralUI.Tests;
+
+public class DataConnectionFormTests : BunitContext
+{
+    private readonly ISiteRepository _siteRepo = Substitute.For<ISiteRepository>();
+
+    public DataConnectionFormTests()
+    {
+        Services.AddSingleton(_siteRepo);
+        AddTestAuth();
+        var sites = new List<Site> { new("Plant-A", "plant-a") { Id = 1 } };
+        _siteRepo.GetAllSitesAsync(Arg.Any<CancellationToken>())
+            .Returns(Task.FromResult<IReadOnlyList<Site>>(sites));
+    }
+
+    private void AddTestAuth()
+    {
+        var claims = new[]
+        {
+            new Claim("Username", "tester"),
+            new Claim(ClaimTypes.Role, "Admin")
+        };
+        var user = new ClaimsPrincipal(new ClaimsIdentity(claims, "TestAuth"));
+        Services.AddSingleton<AuthenticationStateProvider>(new TestAuthStateProvider(user));
+        Services.AddAuthorizationCore();
+    }
+
+    [Fact]
+    public void NoProtocolDropdown_IsRendered()
+    {
+        var cut = Render<DataConnectionForm>(p => p.Add(f => f.SiteId, 1));
+        Assert.DoesNotContain("Custom", cut.Markup);
+        var labels = cut.FindAll("label").Select(l => l.TextContent.Trim()).ToList();
+        Assert.DoesNotContain(labels, l => l == "Protocol");
+    }
+
+    [Fact]
+    public async Task Save_InvalidPrimaryUrl_DoesNotCallRepo()
+    {
+        var cut = Render<DataConnectionForm>(p => p.Add(f => f.SiteId, 1));
+        cut.FindAll("input[type='text']")
+           .First(i => i.GetAttribute("placeholder")?.StartsWith("opc.tcp") == true)
+           .Change("not-a-url");
+
+        // Name field (the first text input that is NOT the OPC URL)
+        cut.FindAll("input[type='text']")
+           .First(i => i.GetAttribute("placeholder") is null
+                       || !i.GetAttribute("placeholder")!.StartsWith("opc.tcp"))
+           .Change("My Connection");
+
+        await cut.FindAll("button")
+                 .First(b => b.TextContent.Trim() == "Save").ClickAsync(new());
+
+        await _siteRepo.DidNotReceive().AddDataConnectionAsync(Arg.Any<DataConnection>());
+        Assert.Contains("Endpoint URL must be a valid", cut.Markup);
+    }
+
+    [Fact]
+    public async Task Save_ValidConfig_PersistsTypedJsonAndProtocolOpcUa()
+    {
+        DataConnection? captured = null;
+        await _siteRepo.AddDataConnectionAsync(
+            Arg.Do<DataConnection>(d => captured = d));
+
+        var cut = Render<DataConnectionForm>(p => p.Add(f => f.SiteId, 1));
+
+        // Name
+        cut.FindAll("input[type='text']")
+           .First(i => i.GetAttribute("placeholder") is null
+                       || !i.GetAttribute("placeholder")!.StartsWith("opc.tcp"))
+           .Change("PLC-1");
+        // Endpoint URL
+        cut.FindAll("input[type='text']")
+           .First(i => i.GetAttribute("placeholder")?.StartsWith("opc.tcp") == true)
+           .Change("opc.tcp://plant-a:4840");
+
+        await cut.FindAll("button")
+                 .First(b => b.TextContent.Trim() == "Save").ClickAsync(new());
+
+        Assert.NotNull(captured);
+        Assert.Equal("OpcUa", captured!.Protocol);
+        Assert.NotNull(captured.PrimaryConfiguration);
+
+        using var doc = JsonDocument.Parse(captured.PrimaryConfiguration!);
+        Assert.Equal("opc.tcp://plant-a:4840",
+            doc.RootElement.GetProperty("endpointUrl").GetString());
+        Assert.Equal(60000,
+            doc.RootElement.GetProperty("sessionTimeoutMs").GetInt32());
+    }
+}