step3/api/QuestionsApi.Tests/FlashcardCsvTests.cs

using QuestionsApi.Services.Flashcards;
using Xunit;

namespace QuestionsApi.Tests;

public sealed class FlashcardCsvTests
{
    [Fact]
    public void ParseRows_HandlesQuotedMultilineFieldsAndEmbeddedCommas()
    {
        var csv = "stable_id,deck,type,prompt,answer,extra,tags,source_question_external_id\n"
            + "abc-1,Cardio,basic,\"What is the first line,\nsecond line?\",\"Answer, with comma\",,tag1;tag2,q-1\n";

        var rows = FlashcardCsv.ParseRows(csv);

        Assert.Equal(2, rows.Count);
        var data = rows[1];
        Assert.Equal("abc-1", data[0]);
        Assert.Equal("What is the first line,\nsecond line?", data[3]);
        Assert.Equal("Answer, with comma", data[4]);
        Assert.Equal("tag1;tag2", data[6]);
    }

    [Fact]
    public void ParseRows_HandlesEscapedDoubleQuotes()
    {
        var csv = "a,b\n\"she said \"\"hi\"\"\",plain\n";

        var rows = FlashcardCsv.ParseRows(csv);

        Assert.Equal("she said \"hi\"", rows[1][0]);
        Assert.Equal("plain", rows[1][1]);
    }

    [Fact]
    public void ParseRows_SupportsUnicodeContent()
    {
        var csv = "a,b\néè中文,\U0001F600\n";

        var rows = FlashcardCsv.ParseRows(csv);

        Assert.Equal("éè中文", rows[1][0]);
        Assert.Equal("😀", rows[1][1]);
    }

    [Fact]
    public void ParseRows_HandlesFileWithoutTrailingNewline()
    {
        var csv = "a,b\n1,2";

        var rows = FlashcardCsv.ParseRows(csv);

        Assert.Equal(2, rows.Count);
        Assert.Equal(["1", "2"], rows[1]);
    }

    [Fact]
    public void WriteRow_QuotesFieldsContainingSpecialCharacters()
    {
        var row = FlashcardCsv.WriteRow(["plain", "has,comma", "has\"quote", "has\nnewline"]);

        Assert.Equal("plain,\"has,comma\",\"has\"\"quote\",\"has\nnewline\"", row);
    }

    [Fact]
    public void WriteThenParse_RoundTrips()
    {
        var original = new[] { "id-1", "Deck, Name", "basic", "prompt with \"quotes\" and\nnewline", "answer", "", "a;b", "q-1" };
        var line = FlashcardCsv.WriteRow(original);

        var rows = FlashcardCsv.ParseRows("header\n" + line + "\n");

        Assert.Equal(original, rows[1]);
    }
}