What is the test for establishing a common boundary?

'* * * The fact that an accurate survey is possible is not conclusive of the question whether a doubt existed as to the location of a common boundary. Thus the doubt may arise from a believed uncertainty which may be proved by direct evidence or inferred from the circumstances surrounding the parties at the time when the agreement is deemed to have been made * * *; and if in good faith the parties resolve their doubt by the practical location of the common boundary it will be considered the boundary called for by the deed.' Mello v. Weaver, 36 Cal.2d 456, 460, 224 P.2d 691, 693.

In Martin v. Lopes, 28 Cal.2d 618, 170 P.2d 881, the statement is made that in order to invoke the doctrine of agreed boundaries all that need be shown is lack of knowledge by both parties of where the line should be drawn.