LetterControlTest.cs

public class LetterControlTest
{
    ...
    [UnityTest]
    public IEnumerator WhenChangeColorControlToGreenThenItIsChanged()
    {
        var colorToChange = ColorCollection.Green;
        _letterControl.ChangeColorControl(colorToChange);
        yield return new WaitForSeconds(0.15f * 11f);
        
        Assert.True(Mathf.Approximately(colorToChange.r, _image.color.r));
        Assert.True(Mathf.Approximately(colorToChange.g, _image.color.g));
        Assert.True(Mathf.Approximately(colorToChange.b, _image.color.b));
        Assert.True(Mathf.Approximately(colorToChange.a, _image.color.a));
    }
}