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

CHANGELOG.md

@@ -14,9 +14,11 @@ 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
+- Added null guards for botMessageChannel and botReleaseMessageChannel parameters in BotService constructor
 ### Changed
 - Dependencies - Updated NSubstitute.Analyzers.CSharp to 1.0.17
 - Switched to use minimal APIs

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 +106,37 @@ await bot.Received(1)
                 );
         }
     }
+
+    public static TheoryData<int, string> NullConstructorArguments =>
+        new()
+        {
+            { 0, "bot" },
+            { 1, "botMessageChannel" },
+            { 2, "botReleaseMessageChannel" },
+        };
+
+    [Theory]
+    [MemberData(nameof(NullConstructorArguments))]
+    public void Constructor_ThrowsArgumentNullException_WhenParameterIsNull(
+        int nullParameterIndex,
+        string expectedParamName
+    )
+    {
+        ConstructorInfo? ctor = typeof(BotService).GetConstructor(
+            [typeof(IDiscordBot), typeof(IMessageChannel<BotMessage>), typeof(IMessageChannel<BotReleaseMessage>)]
+        );
+        Assert.NotNull(ctor);
+
+        object?[] args =
+        [
+            GetSubstitute<IDiscordBot>(),
+            GetSubstitute<IMessageChannel<BotMessage>>(),
+            GetSubstitute<IMessageChannel<BotReleaseMessage>>(),
+        ];
+        args[nullParameterIndex] = null;
+
+        TargetInvocationException ex = Assert.Throws<TargetInvocationException>(() => ctor.Invoke(args));
+        ArgumentNullException ane = Assert.IsType<ArgumentNullException>(ex.InnerException);
+        Assert.Equal(expected: expectedParamName, actual: ane.ParamName);
+    }
 }

src/BuildBot.Discord/Services/BotService.cs

@@ -23,8 +23,9 @@ IMessageChannel<BotReleaseMessage> botReleaseMessageChannel
     )
     {
         this._bot = bot ?? throw new ArgumentNullException(nameof(bot));
-        this._botMessageChannel = botMessageChannel;
-        this._botReleaseMessageChannel = botReleaseMessageChannel;
+        this._botMessageChannel = botMessageChannel ?? throw new ArgumentNullException(nameof(botMessageChannel));
+        this._botReleaseMessageChannel =
+            botReleaseMessageChannel ?? throw new ArgumentNullException(nameof(botReleaseMessageChannel));
 
         this._botMessageChannel.ReadAllAsync(this._cancellationTokenSource.Token)
             .ToObservable()