This paper presents an evaluation of different generation methods of input expressions to definitional interpreters. We compare three different ways of generating expressions of a specified algebraic data type. The approaches that we describe are QuickCheck, SmallCheck and a uniform generation technique, as laid out in their original papers. Subsequently, we illustrate some of the advantages and pitfalls that ought to be considered when using each of the aforementioned approaches. Experimental evaluation shows that the uniform generation method can provide promising results at the expense of time. Compared with this, the QuickCheck and SmallCheck off-the-shelf generation methods are time-efficient, yet lack precision when it comes to generating well-typed terms.