public void TestPreviewOpenCloseFile()
{
using var previewWorkspace = new PreviewWorkspace();
var solution = previewWorkspace.CurrentSolution;
var project = solution.AddProject("project", "project.dll", LanguageNames.CSharp);
var document = project.AddDocument("document", "");
Assert.True(previewWorkspace.TryApplyChanges(document.Project.Solution));
previewWorkspace.OpenDocument(document.Id);
Assert.Equal(1, previewWorkspace.GetOpenDocumentIds().Count());
Assert.True(previewWorkspace.IsDocumentOpen(document.Id));
previewWorkspace.CloseDocument(document.Id);
Assert.Equal(0, previewWorkspace.GetOpenDocumentIds().Count());
Assert.False(previewWorkspace.IsDocumentOpen(document.Id));
}