Test-driven development (TDD) and pair programming (PP) are the key practices of eXtreme Programming methodology that have caught the attention of software engineers and researchers worldwide. One of the aims of the large experiment performed at Wroclaw University of Technology was to investigate the difference between test-driven development and the traditional, test-last develop- ment as well as pair programming and solo programming with respect to the external code quality. It appeared that the external code quality was lower when test-driven development was used instead of the classic, test-last software development approach in case of solo programmers (p=0.028) and pairs (p=0.013). There was no difference in the external code quality when pair programming was used instead of solo programming.