What is the test for determining the best interest of a parent in a custody matter?

First, I refer to the following portions of the summary of law set out in para. 49 of Gordon v. Goertz, by McLachlin J., starting at item 4: … 4. The inquiry [into the child’s best interests] does not begin with a legal presumption in favour of the custodial parent, although the custodial parent's views are entitled to great respect. 5. Each case turns on its own unique circumstances. The only issue is the best interest of the child in the particular circumstances of the case. 6. The focus is on the best interests of the child, not the interests and rights of the parents. 7. More particularly the judge should consider, inter alia: (a) the existing custody arrangement and relationship between the child and the custodial parent; (b) the existing access arrangement and the relationship between the child and the access parent; (c) the desirability of maximizing contact between the child and both parents; (d) the views of the child; (e) the custodial parent’s reason for moving, only in the exceptional case where it is relevant to that parent’s ability to meet the needs of the child; (f) disruption to the child of a change in custody; (g) disruption to the child consequent on removal from family, schools, and the community he or she has come to know.