Make preview check for delivery API content case insensitive. (#18731)

Author: AndyButland

src/Umbraco.Cms.Api.Delivery/Services/RequestPreviewService.cs

@@ -1,4 +1,4 @@
-using Microsoft.AspNetCore.Http;
+using Microsoft.AspNetCore.Http;
 using Umbraco.Cms.Core.DeliveryApi;
 
 namespace Umbraco.Cms.Api.Delivery.Services;
@@ -11,5 +11,5 @@ public RequestPreviewService(IHttpContextAccessor httpContextAccessor)
     }
 
     /// <inheritdoc />
-    public bool IsPreview() => GetHeaderValue("Preview") == "true";
+    public bool IsPreview() => string.Equals(GetHeaderValue("Preview"), "true", StringComparison.OrdinalIgnoreCase);
 }

tests/Umbraco.Tests.UnitTests/Umbraco.Cms.Api.Delivery/Services/RequestPreviewServiceTests.cs

@@ -0,0 +1,31 @@
+using Microsoft.AspNetCore.Http;
+using Moq;
+using NUnit.Framework;
+using Umbraco.Cms.Api.Delivery.Services;
+
+namespace Umbraco.Cms.Tests.UnitTests.Umbraco.Cms.Api.Delivery.Services;
+
+[TestFixture]
+public class RequestPreviewServiceTests
+{
+    [TestCase(null, false)]
+    [TestCase("", false)]
+    [TestCase("false", false)]
+    [TestCase("true", true)]
+    [TestCase("True", true)]
+    public void IsPreview_Returns_Expected_Result(string? headerValue, bool expected)
+    {
+        var httpContext = new DefaultHttpContext();
+        httpContext.Request.Headers["Preview"] = headerValue;
+
+        var httpContextAccessorMock = new Mock<IHttpContextAccessor>();
+        httpContextAccessorMock
+            .Setup(x => x.HttpContext)
+            .Returns(httpContext);
+        var sut = new RequestPreviewService(httpContextAccessorMock.Object);
+
+        var result = sut.IsPreview();
+
+        Assert.AreEqual(expected, result);
+    }
+}