chore(): Enforce mTLS requirement in CreateMtlsHttpClient and update tests

Author: sandy2008

src/OpenTelemetry.Exporter.OpenTelemetryProtocol/Implementation/OtlpMtlsHttpClientFactory.cs

@@ -18,6 +18,8 @@ internal static class OtlpMtlsHttpClientFactory
     /// <param name="mtlsOptions">The mTLS configuration options.</param>
     /// <param name="configureClient">Optional action to configure the client.</param>
     /// <returns>An HttpClient configured for mTLS.</returns>
+    /// <exception cref="ArgumentNullException">Thrown when <paramref name="mtlsOptions"/> is null.</exception>
+    /// <exception cref="InvalidOperationException">Thrown when mTLS is not enabled.</exception>
     public static HttpClient CreateMtlsHttpClient(
         OtlpMtlsOptions mtlsOptions,
         Action<HttpClient>? configureClient = null)
@@ -26,9 +28,9 @@ public static HttpClient CreateMtlsHttpClient(
 
         if (!mtlsOptions.IsEnabled)
         {
-            var client = new HttpClient();
-            configureClient?.Invoke(client);
-            return client;
+            throw new InvalidOperationException(
+                "mTLS options must include a client or CA certificate path."
+            );
         }
 
         HttpClientHandler? handler = null;

test/OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests/OtlpMtlsHttpClientFactoryTests.cs

@@ -13,14 +13,12 @@ namespace OpenTelemetry.Exporter.OpenTelemetryProtocol.Tests;
 public class OtlpMtlsHttpClientFactoryTests
 {
     [Fact]
-    public void CreateHttpClient_ReturnsHttpClient_WhenMtlsIsDisabled()
+    public void CreateHttpClient_ThrowsInvalidOperationException_WhenMtlsIsDisabled()
     {
         var options = new OtlpMtlsOptions(); // Disabled by default
 
-        using var httpClient = OpenTelemetryProtocol.Implementation.OtlpMtlsHttpClientFactory.CreateMtlsHttpClient(options);
-
-        Assert.NotNull(httpClient);
-        Assert.IsType<HttpClient>(httpClient);
+        Assert.Throws<InvalidOperationException>(() =>
+            OpenTelemetryProtocol.Implementation.OtlpMtlsHttpClientFactory.CreateMtlsHttpClient(options));
     }
 
     [Fact]