Add ProxyCommand unit tests for headers and error cases

Added two unit tests to ApiCommandActionTests.cs to verify ProxyCommand behavior with various headers and whitespace paths. Also added System.Text.Json.Nodes using directive for JSON support in tests.

#61

Author: ziagham

tests/SynentraCtl.UnitTests/Commands/ApiCommandActionTests.cs

@@ -10,6 +10,7 @@
 using Synentra.Client.Models.Tokens;
 using SynentraCtl.Commands;
 using SynentraCtl.Core.Services.Logger;
+using System.Text.Json.Nodes;
 
 namespace SynentraCtl.UnitTests.Commands;
 
@@ -496,4 +497,67 @@ public async Task TokenCommand_Generate_Exception_WritesError()
 
         provider.GetRequiredService<ISynentraCtlLogger>().Received().WriteError(Arg.Any<string>());
     }
+
+    [Fact]
+    public async Task ProxyCommand_Create_InvokedWithHeaders_WritesResponse()
+    {
+        var provider = BuildProvider(s =>
+        {
+            var client = Substitute.For<ISynentraClient>();
+            var proxyClient = Substitute.For<ISynentraProxyClient>();
+
+            proxyClient.ExecuteAsync(
+                Arg.Any<string>(), 
+                Arg.Any<string>(), 
+                Arg.Any<JsonNode>(), 
+                Arg.Any<Dictionary<string, string>>(), 
+                Arg.Any<CancellationToken>())
+            .Returns(JsonNode.Parse("{\"status\":\"ok\"}"));
+
+            client.Proxy.Returns(proxyClient);
+            s.AddSingleton(client);
+        });
+
+        var cmd = ProxyCommand.Create(provider);
+        await InvokeAsync(cmd, [
+            "--method", "POST",
+            "--path", "/health",
+            "--body", "{}",
+            "--header", "Authorization:Bearer token",
+            "--header", "InvalidHeader",
+            "--header", "X-Test:123"
+            ]);
+
+        provider.GetRequiredService<ISynentraCtlLogger>().Received().Write(Arg.Is<string>(s => s.Contains("status")));
+    }
+
+    [Fact]
+    public async Task ProxyCommand_WhitespacePath_WritesError()
+    {
+        var provider = BuildProvider(s =>
+        {
+            var client = Substitute.For<ISynentraClient>();
+            var proxyClient = Substitute.For<ISynentraProxyClient>();
+
+            proxyClient.ExecuteAsync(
+                Arg.Any<string>(),
+                Arg.Any<string>(),
+                Arg.Any<JsonNode>(),
+                Arg.Any<Dictionary<string, string>>(),
+                Arg.Any<CancellationToken>())
+            .Throws(new Exception("server error"));
+
+            client.Proxy.Returns(proxyClient);
+            s.AddSingleton(client);
+        });
+
+        var cmd = ProxyCommand.Create(provider);
+        await InvokeAsync(cmd, [
+            "--path", " ",
+            "--body", "{}",
+            "--header", "A:1"
+            ]);
+
+        provider.GetRequiredService<ISynentraCtlLogger>().Received().WriteError(Arg.Any<string>());
+    }
 }