public void GetWords_ReturnExpectedCollection_IfAllWordsIsNew() {
// Arrange
AddWord(10, LearningLevel.New);
const int wordInExercise = 10;
// Act
var result = Planner.GetWords(wordInExercise);
// Assert
result.Should().HaveCount(wordInExercise);
IsCollectionContainsDuplicates(result).Should().BeFalse("collection shouldn't contains duplicates");
result.ShouldBeEquivalentTo(Words);
}