test(discord): Add null-guard branch coverage for BotService constructor

CHANGELOG.md

@@ -14,6 +14,7 @@ Please ADD ALL Changes to the UNRELEASED SECTION and not a specific release
 - BuildBot.Json.Tests: new test project covering BuildBot.Json at 100% line and branch coverage
 - BuildBot.ServiceModel.Tests: Added test coverage for all types in BuildBot.ServiceModel
 - BuildBot.Discord.Tests: Added unit tests to increase code coverage to 100%
+- BotService null-guard branch coverage test
 ### Fixed
 - Suppress known Scriban 6.2.0 vulnerabilities pending upgrade
 - SnsMessage: Token property was never populated from the constructor argument

src/BuildBot.Discord.Tests/Services/BotServiceTests.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Reflection;
 using System.Threading;
 using System.Threading.Tasks;
 using BuildBot.Discord.Models;
@@ -105,4 +106,17 @@ await bot.Received(1)
                 );
         }
     }
+
+    [Fact]
+    public void Constructor_ThrowsArgumentNullException_WhenBotIsNull()
+    {
+        ConstructorInfo? ctor = typeof(BotService).GetConstructor(
+            [typeof(IDiscordBot), typeof(IMessageChannel<BotMessage>), typeof(IMessageChannel<BotReleaseMessage>)]
+        );
+        Assert.NotNull(ctor);
+
+        TargetInvocationException ex = Assert.Throws<TargetInvocationException>(() => ctor.Invoke([null, null, null]));
+        ArgumentNullException ane = Assert.IsType<ArgumentNullException>(ex.InnerException);
+        Assert.Equal(expected: "bot", actual: ane.ParamName);
+    }
 }