test: add ApiClientBaseTests with 200 OK mapping test

NEW/tests/JdeScoping.Client.Tests/Services/ApiClientBaseTests.cs

@@ -0,0 +1,39 @@
+using System.Net;
+using System.Text.Json;
+using JdeScoping.Core.ApiContracts.Results;
+using RichardSzalay.MockHttp;
+using Shouldly;
+
+namespace JdeScoping.Client.Tests.Services;
+
+public class ApiClientBaseTests
+{
+    private readonly MockHttpMessageHandler _mockHttp;
+    private readonly TestableApiClient _client;
+
+    public ApiClientBaseTests()
+    {
+        _mockHttp = new MockHttpMessageHandler();
+        var httpClient = new HttpClient(_mockHttp) { BaseAddress = new Uri("http://localhost/") };
+        _client = new TestableApiClient(httpClient);
+    }
+
+    public record TestDto(int Id, string Name);
+
+    [Fact]
+    public async Task GetAsync_Returns200_MapsToSuccessValue()
+    {
+        // Arrange
+        var expected = new TestDto(42, "Test");
+        _mockHttp.When("/api/test")
+            .Respond("application/json", JsonSerializer.Serialize(expected));
+
+        // Act
+        var result = await _client.GetAsync<TestDto>("/api/test");
+
+        // Assert
+        result.IsSuccess.ShouldBeTrue();
+        result.Value.Id.ShouldBe(42);
+        result.Value.Name.ShouldBe("Test");
+    }
+}