Tests: add tests to cover cases that functions gives ValueError - 1) when unknow fit is given; 2) when min_signal is smaller than 0; 3) when given mask as a different shape to data
Tests: add tests to cover cases that functions gives ValueError - 1) when unknow fit is given; 2) when min_signal is smaller than 0; 3) when given mask as a different shape to data

matthieudumont/dipy,JohnGriffiths/dipy,villalonreina/dipy,nilgoyyou/dipy,JohnGriffiths/dipy,StongeEtienne/dipy,matthieudumont/dipy,FrancoisRheaultUS/dipy,demianw/dipy,StongeEtienne/dipy,nilgoyyou/dipy,villalonreina/dipy,FrancoisRheaultUS/dipy,demianw/dipy