What is the test for a frivolous claim?

Ontario, Canada

The following excerpt is from Rozen v. Jones, 2009 CanLII 31183 (ON SC):

As noted by Grange J. in Paquette v. Cruji[4],: The law will always protect a defendant from a frivolous action but it should not deprive a plaintiff of his cause of action, ostensibly valid, where the particulars are not within his knowledge and are well within those of the defendant.

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