Temporary Faith

Could a Calvinist tell me how the teaching of "Temporary Faith" doesn't undermine assurance?

From Turretin Fan's blog post:

There is a temporary faith, that goes beyond all the former, and is effected by the common operation of the Spirit of God: nor is it merely taken up with the truth of the gospel, but also hath some relish of the goodness and sweetness of it; and hence the stonyground hearers are said to receive the word with joy, Matthew xiii. 20.; yet this belief hath no root, no abiding principle: it is not the faith of the promise that takes place in the children of promise.—Here is the most subtile deceit in the matter of faith: some people may take hold of Christ, as it were, and really get some sap and virtue from him, for their refreshment, and yet never get in to him. They are like the ivy, that grows up by the tree, and clasps about the tree, and draws sap from the tree, and yet grows upon its own root, and is never one and the same with the tree: so here, some professors may receive Christ, in the promise, by a temporary faith, they clasp about him closely, and draw some sap and virtue from him; but still they are never rooted in Christ, but rooted in the old Adam; still rooted in the old covenant, were never cut off from the old root, and ingrafted into Christ, but only draw virtue from Christ to maintain their old-covenant fruit.

Why I bring this up is not to convince the Reformed that the Calvinist system does not actually offer assurance, but to show that what I was saying about Calvinist assurance is true from within Calvinism itself.

If one can have "temporary faith" and believe one is elect when one is not, how does any Calvinist show to himself that his faith is "true" faith?

If a Calvinist points to the Gospel that begs the question, for even Ralph Erskine points his readers to the quality of their faith to differentiate "temporaary faith" from "true" faith:

Temporary faith may say, From the Lord I have righteousness and strength; but true faith says, "In the Lord have I righteousness and strength."—Temporary faith may get many things from him, but true faith gets all things in him, and is complete in him.

So how does one know aside from a sematic shift wheter "In the Lord I have righteousness.." (true faith) or "From the Lord I have righteousness..." for example?

I suspect it is by looking at the quality of one's faith, because if the right quality is not there one does not have "true" faith and the promises to not pertain.

Which is what I have been saying all along.