To test fruit for pectin, mix 1 teaspoon of cooked fruit with 1 tablespoon of rubbing alcohol. If the mixture coagulates into a single clump, there is sufficient pectin. (Do not taste the mixture, since rubbing alcohol is poisonous!) 

To check fruit for acidity, compare its taste to that of a mixture consisting of 3 tablespoons of water, 1 teaspoon of lemon juice, and 1/2 teaspoon of sugar. If the fruit is less tart than the lemon juice mixture, it needs more acid (often in the form of lemon juice or citric acid crystals). 

Another way to test for acidity is to use pH paper. Some garden stores will carry pH paper strips to test soil, but these can also be used for testing acidity of jams and jellies. If you can’t locate pH paper in your garden store you can always find it online.