fix: ensure process output pipe is drained by caller

src/process.tests/NullPipeConcurrencyTests.cs

@@ -0,0 +1,59 @@
+// Copyright (c) The Geekeey Authors
+// SPDX-License-Identifier: EUPL-1.2
+
+namespace Geekeey.Process.Tests;
+
+internal sealed class NullPipeConcurrencyTests
+{
+	// A process writing enough output to fill its pipe can receive SIGPIPE if the read end is closed too early.
+	// Run many chatty processes at once to make premature pipe closure observable and to exercise pipe lifetime
+	// while processes are being started and completed concurrently.
+	// Test both the default targets and explicitly configured null targets, since both must keep consuming
+	// process output until the process exits.
+
+	[Test]
+	public async Task Chatty_commands_can_run_concurrently_with_default_null_output_pipes()
+	{
+		var commands = new List<Command>();
+
+		for (var i = 0; i < 64; i++)
+		{
+			commands.Add(new Command(Testing.Fixture.Program.FilePath)
+				.WithArguments(["generate", "clob", "--length", "100000", "--lines", "2"]));
+		}
+
+		var results = await Task.WhenAll(commands.Select(async command => await command.ExecuteAsync()));
+
+		using (Assert.Multiple())
+		{
+			foreach (var result in results)
+			{
+				await Assert.That(result.ExitCode).IsZero();
+			}
+		}
+	}
+
+	[Test]
+	public async Task Chatty_commands_can_run_concurrently_with_explicit_null_output_pipes()
+	{
+		var commands = new List<Command>();
+
+		for (var i = 0; i < 64; i++)
+		{
+			commands.Add(new Command(Testing.Fixture.Program.FilePath)
+				.WithArguments(["generate", "clob", "--length", "100000", "--lines", "2"])
+				.WithStandardOutputPipe(PipeTarget.Null)
+				.WithStandardErrorPipe(PipeTarget.Null));
+		}
+
+		var results = await Task.WhenAll(commands.Select(async command => await command.ExecuteAsync()));
+
+		using (Assert.Multiple())
+		{
+			foreach (var result in results)
+			{
+				await Assert.That(result.ExitCode).IsZero();
+			}
+		}
+	}
+}