The term test envelop refers to the limits of what can actually be tested in a particular research project. If you've ever heard the phrase "push the envelope," it means to expand the limits or push the boundaries of what is possible.
Test points refer to the specific items that are being tested in a particular research experiment or test. For example, some test points for an individual being assessed for Attention Deficit Hyperactivity Disorder (ADHD) are impulsivity and bordem.
Finally, test range refers to how much of something can be tested. Don't get this confused with test envelop; test envelope refers to the broader and more general limits of a test, while the test range refers to the level of specific points that can be measured.