The term grammar-based software describes software whose input can be specified by a context-free grammar. This grammar may occur explicitly in the software, in the form of an input specification to a parser generator, or implicitly, in the form of a hand-written parser. Grammar-based software includes not only programming language compilers, but also tools for program analysis, reverse en- gineering, software metrics and documentation generation. Hence, ensuring their completeness and correctness is a vital prerequisite for their use. In this paper we propose a strategy for the construction of test suites for grammar based software, and illustrate this strategy using the ISO C++ grammar. We use the concept of grammar- rule coverage as a pivot for the reduction of an implementation-based test suite, and demonstrate a significant decrease in the size of this suite. The effectiveness of this reduced test suite is compared to the original test suite with respect to code coverage and more importantly, fault detection. This work greatly expands upon previous work in this area and utilises large scale mutation testing to compare the effectiveness of grammar-rule coverage to that of statement coverage as a reduction criterion for test suites of grammar-based software. This work finds that when grammar rule coverage is used as the sole criterion for reducing test suites of grammar based software, the fault detection capability of that reduced test suite is greatly diminished when compared to other coverage criteria such as statement coverage