// Copyright (c) Sbroenne. All rights reserved.
// Licensed under the MIT License.
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Hosting;
using Xunit;
namespace Sbroenne.ExcelMcp.McpServer.Tests.Unit;
/// <summary>
/// Regression tests for MCP Server configuration.
///
/// Bug 8 (Feb 2026): Host.CreateApplicationBuilder() enables reloadOnChange:true by default,
/// creating a FileSystemWatcher for appsettings.json. Under file I/O storms from Excel
/// (temp files, lock files), this watcher fires ParseEventBufferAndNotifyForEach in a tight
/// loop on the threadpool, consuming ~85% CPU.
///
/// These tests ensure that config reload watchers are permanently disabled.
/// </summary>
[Trait("Category", "Unit")]
[Trait("Speed", "Fast")]
[Trait("Layer", "McpServer")]
[Trait("Feature", "Configuration")]
public class ConfigurationReloadTests
{
/// <summary>
/// REGRESSION TEST: No configuration source should use reloadOnChange:true.
/// This caused 85% CPU from FileSystemWatcher under I/O storms (Bug 8).
/// </summary>
[Fact]
public void Configuration_NoFileSource_HasReloadOnChangeEnabled()
{
// Arrange — build the host the same way Program.Main does
var builder = Host.CreateApplicationBuilder([]);
// Replicate Program.cs config setup
builder.Configuration.Sources.Clear();
builder.Configuration
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: false)
.AddJsonFile($"appsettings.{builder.Environment.EnvironmentName}.json", optional: true, reloadOnChange: false)
.AddEnvironmentVariables()
.AddCommandLine([]);
// Act — inspect all configuration sources for file-based sources with reload enabled
var fileSourcesWithReload = builder.Configuration.Sources
.OfType<Microsoft.Extensions.Configuration.Json.JsonConfigurationSource>()
.Where(s => s.ReloadOnChange)
.ToList();
// Assert
Assert.Empty(fileSourcesWithReload);
}
/// <summary>
/// REGRESSION TEST: After clearing default sources, environment variables must still be available.
/// The initial Bug 8 fix (Sources.Clear()) was too aggressive — it removed env vars and CLI args.
/// </summary>
[Fact]
public void Configuration_AfterClear_EnvironmentVariablesAreAvailable()
{
// Arrange
var builder = Host.CreateApplicationBuilder([]);
builder.Configuration.Sources.Clear();
builder.Configuration
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: false)
.AddJsonFile($"appsettings.{builder.Environment.EnvironmentName}.json", optional: true, reloadOnChange: false)
.AddEnvironmentVariables()
.AddCommandLine([]);
// Act — environment variables should be accessible
// PATH is a universally available env var on Windows
var pathValue = builder.Configuration["PATH"] ?? builder.Configuration["Path"];
// Assert — if env vars weren't re-added, this would be null
Assert.NotNull(pathValue);
}
/// <summary>
/// REGRESSION TEST: After clearing default sources, command-line arguments must still work.
/// </summary>
[Fact]
public void Configuration_AfterClear_CommandLineArgsAreAvailable()
{
// Arrange
var builder = Host.CreateApplicationBuilder(["--TestKey=TestValue"]);
builder.Configuration.Sources.Clear();
builder.Configuration
.AddJsonFile("appsettings.json", optional: true, reloadOnChange: false)
.AddJsonFile($"appsettings.{builder.Environment.EnvironmentName}.json", optional: true, reloadOnChange: false)
.AddEnvironmentVariables()
.AddCommandLine(["--TestKey=TestValue"]);
// Act
var value = builder.Configuration["TestKey"];
// Assert
Assert.Equal("TestValue", value);
}
/// <summary>
/// Verify that the default Host.CreateApplicationBuilder() DOES enable reloadOnChange.
/// This proves our fix is necessary — without it, file watchers would be created.
/// </summary>
[Fact]
public void DefaultBuilder_HasReloadOnChange_True()
{
// Arrange — build with defaults (no clearing)
var builder = Host.CreateApplicationBuilder([]);
// Act — check default JSON sources
var jsonSourcesWithReload = builder.Configuration.Sources
.OfType<Microsoft.Extensions.Configuration.Json.JsonConfigurationSource>()
.Where(s => s.ReloadOnChange)
.ToList();
// Assert — defaults SHOULD have reloadOnChange:true (this is what we're fixing)
Assert.NotEmpty(jsonSourcesWithReload);
}
}
