1. A method of generating test cases for a text annotator which searches text documents and analyzes them relative to a defined set of tags comprising: receiving a corpus of text fragments without any annotations and a description of the text annotator, by executing first instructions in a computer system; determining types of inputs to the text annotator from the description, the types of inputs including at least one phrase selected from the group consisting of a person phrase, a date phrase, and a diagnosis phrase, by executing second instructions in the computer system; analyzing language structures in the corpus to identify sentence types and grammar constructs, the sentence types including at least one sentence selected from the group consisting of a question, a command, a compound sentence, and a conditional sentence, and wherein said analyzing includes performing a slot grammar parse of the corpus to determine various parse trees of the corpus including a most common parse tree, by executing third instructions in the computer system; generating a first test case by performing a grammar tree transformation on a first selected fragment of the corpus based on the sentence types and the grammar constructs wherein the first selected fragment is selected in response to a selection bias towards a sentence type which corresponds to the most common parse tree of the corpus, by executing fourth instructions in the computer system; and generating a second test case by replacing at least one starting phrase in the first test case with a substitute phrase from at least one dictionary associated with one of the types of inputs that corresponds to the starting phrase, by executing fifth instructions in the computer system.
5. The method of claim 1 wherein the dictionary includes a false synonym for the one input type that corresponds to the starting phrase.