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

In any custody determination, a primary consideration in determining the child's best interest is the goal of assuring stability and continuity. (Burchard v. Garay (1986) 42 Cal.3d 531, 538, and fn. 6, 229 Cal.Rptr. 800, 724 P.2d 486.) "When custody continues over a significant period, the child's need for continuity and stability assumes an increasingly important role. That need will often dictate the conclusion that maintenance of the current arrangement would be in the best interests of that child." (Ibid., fn. omitted; see also In re Marriage of McGinnis (1992) 7 Cal.App.4th 473, 478, 9 Cal.Rptr.2d 182.)