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.