Isolate DiffRunnerTests from the machine's queue owner

docs/diff-tool.custom.md

@@ -53,7 +53,7 @@ New tools are added to the top of the order, the last tool added will resolve be
 ```cs
 await DiffRunner.LaunchAsync(tempFile, targetFile);
 ```
-<sup><a href='/src/DiffEngine.Tests/DiffRunnerTests.cs#L70-L74' title='Snippet source file'>snippet source</a> | <a href='#snippet-DiffRunnerLaunch' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/DiffEngine.Tests/DiffRunnerTests.cs#L92-L96' title='Snippet source file'>snippet source</a> | <a href='#snippet-DiffRunnerLaunch' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 Alternatively the instance  returned from `AddTool*` can be used to explicitly launch that tool.

readme.md

@@ -108,7 +108,7 @@ A tool can be launched using the following:
 ```cs
 await DiffRunner.LaunchAsync(tempFile, targetFile);
 ```
-<sup><a href='/src/DiffEngine.Tests/DiffRunnerTests.cs#L70-L74' title='Snippet source file'>snippet source</a> | <a href='#snippet-DiffRunnerLaunch' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/DiffEngine.Tests/DiffRunnerTests.cs#L92-L96' title='Snippet source file'>snippet source</a> | <a href='#snippet-DiffRunnerLaunch' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 Note that this method will respect the above [difference behavior](/docs/diff-tool.md#detected-difference-behavior) in terms of Auto refresh and MDI behaviors.
@@ -123,7 +123,7 @@ A tool can be closed using the following:
 ```cs
 DiffRunner.Kill(file1, file2);
 ```
-<sup><a href='/src/DiffEngine.Tests/DiffRunnerTests.cs#L84-L88' title='Snippet source file'>snippet source</a> | <a href='#snippet-DiffRunnerKill' title='Start of snippet'>anchor</a></sup>
+<sup><a href='/src/DiffEngine.Tests/DiffRunnerTests.cs#L106-L110' title='Snippet source file'>snippet source</a> | <a href='#snippet-DiffRunnerKill' title='Start of snippet'>anchor</a></sup>
 <!-- endSnippet -->
 
 Note that this method will respect the above [difference behavior](/docs/diff-tool.md#detected-difference-behavior) in terms of MDI behavior.

src/DiffEngine.Tests/DiffRunnerTests.cs

@@ -7,6 +7,28 @@ public class DiffRunnerTests
     static string SourceDirectory { get; } = Path.GetDirectoryName(GetSourceFile())!;
     static string GetSourceFile([CallerFilePath] string path = "") => path;
 
+    // Launching registers a real pending move of file1 over file2 with whatever owns the queue on
+    // this machine, usually the developer's tray. Accepting it moves file1, and discarding it
+    // deletes file1 and then its directory. Run against the source directory that quietly destroys
+    // the checked in fixtures, so the tests get copies instead.
+    // One directory for the whole class, because IsRunning matches the exact command string and
+    // WaitForRunning is also used at test start to wait out the previous test's kill, both of which
+    // want the same paths across tests. Fresh per run, so a FakeDiffTool left behind by a crashed
+    // earlier run cannot match this run's command.
+    static string TempDirectory { get; } = Path.Combine(
+        Path.GetTempPath(),
+        "DiffEngine.DiffRunnerTests",
+        Guid.NewGuid().ToString("N"));
+
+    [After(Class)]
+    public static void DeleteTempDirectory()
+    {
+        if (Directory.Exists(TempDirectory))
+        {
+            Directory.Delete(TempDirectory, true);
+        }
+    }
+
     static ResolvedTool tool;
     string file2;
     string file1;
@@ -216,11 +238,21 @@ async Task WaitForRunning(bool expected)
 
     public DiffRunnerTests()
     {
-        file1 = Path.Combine(SourceDirectory, "DiffRunner.file1.txt");
-        file2 = Path.Combine(SourceDirectory, "DiffRunner.file2.txt");
+        file1 = CopyFixture("DiffRunner.file1.txt");
+        file2 = CopyFixture("DiffRunner.file2.txt");
         command = tool.BuildCommand(file1, file2);
     }
 
+    // Per test rather than per class: a discard deletes the temp file and its directory, so the
+    // copies have to be put back for the test that follows.
+    static string CopyFixture(string name)
+    {
+        Directory.CreateDirectory(TempDirectory);
+        var target = Path.Combine(TempDirectory, name);
+        File.Copy(Path.Combine(SourceDirectory, name), target, true);
+        return target;
+    }
+
     static DiffRunnerTests() =>
         tool = DiffTools.AddTool(
             name: "FakeDiffTool",

src/DiffEngine.Tests/ModuleInitializer.cs

@@ -1,10 +1,44 @@
-public static class ModuleInitializer
+// DiffEngineTray is the obsolete public shim, but its IsRunning is still where the tray check lives.
+#pragma warning disable CS0618
+
+using System.Net;
+using System.Net.Sockets;
+
+public static class ModuleInitializer
 {
     [ModuleInitializer]
     public static void Initialize()
     {
         FileExtensions.AddTextFileConvention(_ => _.EndsWith(".txtConvention".AsSpan()));
         Logging.Enable();
         DiffRunner.Disabled = false;
+        DetachFromPendingFileSurfaces();
+    }
+
+    /// <summary>
+    /// Launching sends a real pending move to whatever owns the queue on this machine. On a
+    /// developer box that is the tray, started at login, and an accept or discard from it kills the
+    /// diff tool process DiffRunnerTests is asserting on. Being inconclusive when a tray is running
+    /// would mean those tests never run locally, so cut both routes instead: no tray, and a viewer
+    /// port nothing is listening on.
+    /// <para>
+    /// A failed move send is the end of the road in <c>PendingFiles.AddMove</c>, and only a delete
+    /// launches a viewer, which nothing here adds. So the moves these tests produce go nowhere and
+    /// no process outside the test can see them.
+    /// </para>
+    /// <para>
+    /// The cost is that the real piper send is not covered from here. That belongs with a tray
+    /// under test control, which is what DiffEngineTray.Tests/DiffRunnerCanKillTest does.
+    /// </para>
+    /// </summary>
+    static void DetachFromPendingFileSurfaces()
+    {
+        DiffEngineTray.IsRunning = false;
+
+        var listener = new TcpListener(IPAddress.Loopback, 0);
+        listener.Start();
+        var port = ((IPEndPoint) listener.LocalEndpoint).Port;
+        listener.Stop();
+        Environment.SetEnvironmentVariable(ViewerClient.PortVariable, port.ToString());
     }
 }