public void BuildToken_ReturnsStringOfProcessedChars(string testString, int chars)
{
//set up
using var builder = new TokenBuilder(testString.GetEnumerator());
//act
for (int i = 0; i <= chars; i++)
{
builder.MoveNext();
}
//test
Assert.AreEqual(testString.Substring(0, chars), builder.CollectPreceding());
}