Indexer with tests

IndexTests.cs

public class Indexer
{
    private readonly Dictionary<string, List<string>> terms =
        new Dictionary<string, List<string>>(StringComparer.OrdinalIgnoreCase);
    private readonly Dictionary<string, List<string>> docsTerms =
        new Dictionary<string, List<string>>(StringComparer.OrdinalIgnoreCase);

    public void Index(string docId, string text)
    {
        List<string> docTerms;
        if (docsTerms.TryGetValue(docId, out docTerms) == false)
        {
            docTerms = new List<string>();
            docsTerms[docId] = docTerms;
        }

        foreach (var docTerm in docTerms)
        {
            terms.Remove(docTerm);
        }

        var words = text.Split();
        foreach (var term in words)
        {
            List<string> val;
            if (terms.TryGetValue(term, out val) == false)
            {
                val = new List<string>();
                terms[term] = val;
            }

            val.Add(docId);
            docTerms.Add(term);
        }
    }

    public List<string> Query(string term)
    {
        List<string> val;
        terms.TryGetValue(term, out val);
        return val ?? new List<string>();
    }

    public void Delete(string docId)
    {
        var docTerms = docsTerms[docId];
        foreach (var term in docTerms)
        {
            terms.Remove(term);
        }
    }
}

[TestFixture]
public class IndexTests
{
    [Test]
    public void CanIndexAndQuery()
    {
        var index = new Indexer();
        index.Index("users/1", "Daniel Lidstrom");
        index.Index("users/2", "index tests");

        Assert.Contains("users/1", index.Query("lidstrom"));
        Assert.Contains("users/2", index.Query("tests"));
    }

    [Test]
    public void CanUpdate()
    {
        var index = new Indexer();
        index.Index("users/1", "Daniel Lidstrom");

        // updating
        index.Index("users/1", "Lars Nilsson");

        Assert.Contains("users/1", index.Query("nilsson"));
        Assert.That(index.Query("lidstrom"), Is.Empty);
    }

    [Test]
    public void CanDelete()
    {
        var index = new Indexer();
        index.Index("users/1", "Daniel Lidstrom");

        // deleting
        index.Delete("users/1");

        Assert.That(index.Query("lidstrom"), Is.Empty);
    }
}