Add integration tests for nonexistent package caching and invalid log file path

requirements.yaml

@@ -106,6 +106,7 @@ sections:
             tests:
               - Context_Create_LogFlag_OpensLogFile
               - IntegrationTest_LogFlag_WritesOutputToFile
+              - IntegrationTest_LogFlag_WithInvalidFilename_ReturnsError
 
           - id: NC-CLI-008
             title: The tool shall cache NuGet packages specified as [package-name]:[version] arguments.
@@ -127,6 +128,7 @@ sections:
               - Context_WriteError_SetsErrorExitCode
               - Context_WriteError_NotSilent_WritesToConsole
               - IntegrationTest_UnknownArgument_ReturnsError
+              - IntegrationTest_CacheNonexistentPackage_ReturnsError
 
           - id: NC-CLI-010
             title: The tool shall reject unknown or malformed command-line arguments with a descriptive error.

test/DemaConsulting.NuGet.CacheTool.Tests/IntegrationTests.cs

@@ -268,4 +268,44 @@ public void IntegrationTest_CachePackage_OutputsPath()
         Assert.IsFalse(string.IsNullOrWhiteSpace(output));
         Assert.DoesNotContain("Error", output);
     }
+
+    /// <summary>
+    ///     Test that attempting to cache a nonexistent package returns an error.
+    /// </summary>
+    [TestMethod]
+    public void IntegrationTest_CacheNonexistentPackage_ReturnsError()
+    {
+        // Act
+        var exitCode = Runner.Run(
+            out var output,
+            "dotnet",
+            _dllPath,
+            "DemaConsulting.NonExistent.Package.XYZ:99.99.99");
+
+        // Assert
+        Assert.AreNotEqual(0, exitCode);
+        Assert.Contains("Error", output);
+    }
+
+    /// <summary>
+    ///     Test that specifying an invalid log file path returns an error.
+    /// </summary>
+    [TestMethod]
+    public void IntegrationTest_LogFlag_WithInvalidFilename_ReturnsError()
+    {
+        // Arrange - use a hard-coded path into a nonexistent directory to ensure failure
+        const string invalidLogPath = "/nonexistent_dir_xyz_abc/invalid.log";
+
+        // Act
+        var exitCode = Runner.Run(
+            out var output,
+            "dotnet",
+            _dllPath,
+            "--log",
+            invalidLogPath);
+
+        // Assert
+        Assert.AreNotEqual(0, exitCode);
+        Assert.Contains("Error", output);
+    }
 }