Write Powerful Rust Macros

6 Testing a builder macro

This chapter covers

• Writing a derive macro that will generate a builder for structs
• Creating white-box tests to verify the behavior of functions within your macro
• Using black-box tests that take an outside view of your code
• Deciding what types of tests are most useful for your macro

The builder pattern is a very convenient, fluent way of constructing structs. Because of that, it is omnipresent in Rust code. Often, though, the code required to write a builder is boilerplate—boilerplate that we can automate away! In this chapter, we will write a macro to do just that. Because we are not touching the original struct, we can use a derive macro (remember, go for the simplest option). In an implementation block, we ...