public void ExecuteSetsDocumentMetadataManagerFilterStringToEmptyString()
        {
            // Arrange

            var manager = Mock.Of <IDocumentMetadataManager>();
            var command = new ClearFilterString(manager);

            // Act

            command.Execute(null);

            // Assert

            Mock.Get(manager).VerifySet(m =>
                                        m.FilterString = string.Empty,
                                        Times.Once);
        }