ersatztv/ErsatzTV.Mcp.Tests/BoundedLineReaderTests.cs

using System.Text;
using ErsatzTV.Mcp;
using NUnit.Framework;
using Shouldly;

namespace ErsatzTV.Mcp.Tests;

[TestFixture]
public class BoundedLineReaderTests
{
    [Test]
    public async Task ReadLineAsync_Should_Return_Line_Without_Trailing_Newline()
    {
        using var reader = new StringReader("hello world\n");

        BoundedLineReader.Line line = await BoundedLineReader.ReadLineAsync(reader, 1024);

        line.EndOfStream.ShouldBeFalse();
        line.Overflowed.ShouldBeFalse();
        line.Text.ShouldBe("hello world");
    }

    [Test]
    public async Task ReadLineAsync_Should_Return_Line_Of_Exactly_Cap_Length_Intact()
    {
        // The cap is the inclusive max: a line of exactly `cap` chars is returned, not overflowed.
        using var reader = new StringReader("abcdefgh\n");

        BoundedLineReader.Line line = await BoundedLineReader.ReadLineAsync(reader, 8);

        line.Overflowed.ShouldBeFalse();
        line.Text.ShouldBe("abcdefgh");
    }

    [Test]
    public async Task ReadLineAsync_Should_Strip_Carriage_Return_In_Crlf()
    {
        using var reader = new StringReader("hello\r\n");

        BoundedLineReader.Line line = await BoundedLineReader.ReadLineAsync(reader, 1024);

        line.Text.ShouldBe("hello");
    }

    [Test]
    public async Task ReadLineAsync_Should_Signal_End_Of_Stream()
    {
        using var reader = new StringReader(string.Empty);

        BoundedLineReader.Line line = await BoundedLineReader.ReadLineAsync(reader, 1024);

        line.EndOfStream.ShouldBeTrue();
    }

    [Test]
    public async Task ReadLineAsync_Should_Overflow_And_Not_Buffer_Oversized_Line()
    {
        // A line far longer than the cap must be reported overflowed with no buffered text —
        // the memory-exhaustion guard.
        string oversized = new string('x', 10_000) + "\n";
        using var reader = new StringReader(oversized);

        BoundedLineReader.Line line = await BoundedLineReader.ReadLineAsync(reader, 16);

        line.EndOfStream.ShouldBeFalse();
        line.Overflowed.ShouldBeTrue();
        line.Text.ShouldBeEmpty();
    }

    [Test]
    public async Task ReadLineAsync_Should_Keep_Subsequent_Lines_Aligned_After_Overflow()
    {
        // After draining an oversized line, the next line must still be read intact.
        var content = new StringBuilder()
            .Append(new string('x', 100)).Append('\n')
            .Append("good\n")
            .ToString();
        using var reader = new StringReader(content);

        BoundedLineReader.Line first = await BoundedLineReader.ReadLineAsync(reader, 16);
        BoundedLineReader.Line second = await BoundedLineReader.ReadLineAsync(reader, 16);

        first.Overflowed.ShouldBeTrue();
        second.Overflowed.ShouldBeFalse();
        second.Text.ShouldBe("good");
    }
}