**Course Title:** Mastering Rust: From Basics to Systems Programming **Section Title:** Testing and Documentation in Rust **Topic:** Write tests for a Rust application and document the code appropriately. (Lab topic) **Objective:** In this lab topic, we will put into practice the concepts learned in the previous topic on testing and documentation in Rust. We will write tests for a Rust application and document the code using Rust's documentation features. **Materials Needed:** * A computer with Rust installed * A text editor or IDE * The code provided in this topic **Step 1: Setting up the Project** To begin, we will create a new Rust project using Cargo. Open your terminal and run the following command: ```bash cargo new calculator --lib ``` This will create a new library project called `calculator`. Navigate into the project directory: ```bash cd calculator ``` **Step 2: Writing the Calculator Library** We will now create a simple calculator library with functions for addition, subtraction, multiplication, and division. Open the `src/lib.rs` file and add the following code: ```rust pub struct Calculator { a: f64, b: f64, } impl Calculator { pub fn new(a: f64, b: f64) -> Calculator { Calculator { a, b } } pub fn add(&self) -> f64 { self.a + self.b } pub fn subtract(&self) -> f64 { self.a - self.b } pub fn multiply(&self) -> f64 { self.a * self.b } pub fn divide(&self) -> f64 { if self.b == 0.0 { panic!("Cannot divide by zero!"); } self.a / self.b } } ``` This library provides a `Calculator` struct with methods for arithmetic operations. **Step 3: Writing Tests** We will now write tests for the `Calculator` library. Open the `tests` directory and create a new file called `calculator_tests.rs`. Add the following code: ```rust #[cfg(test)] mod tests { use super::*; #[test] fn test_add() { let calculator = Calculator::new(10.0, 5.0); assert_eq!(calculator.add(), 15.0); } #[test] fn test_subtract() { let calculator = Calculator::new(10.0, 5.0); assert_eq!(calculator.subtract(), 5.0); } #[test] fn test_multiply() { let calculator = Calculator::new(10.0, 5.0); assert_eq!(calculator.multiply(), 50.0); } #[test] fn test_divide() { let calculator = Calculator::new(10.0, 5.0); assert_eq!(calculator.divide(), 2.0); } #[test] #[should_panic(expected = "Cannot divide by zero!")] fn test_divide_by_zero() { let calculator = Calculator::new(10.0, 0.0); calculator.divide(); } } ``` These tests cover all the methods of the `Calculator` library, including the division by zero case. **Step 4: Documenting the Code** We will now document the `Calculator` library using Rust's documentation features. Open the `src/lib.rs` file and add the following code: ```rust /// A simple calculator library. /// /// This library provides methods for basic arithmetic operations. pub struct Calculator { /// The first operand. a: f64, /// The second operand. b: f64, } impl Calculator { /// Creates a new `Calculator` instance. /// /// # Arguments /// /// * `a` - The first operand. /// * `b` - The second operand. /// /// # Returns /// /// A new `Calculator` instance. pub fn new(a: f64, b: f64) -> Calculator { Calculator { a, b } } /// Adds the two operands. /// /// # Returns /// /// The sum of the two operands. pub fn add(&self) -> f64 { self.a + self.b } /// Subtracts the second operand from the first. /// /// # Returns /// /// The difference between the two operands. pub fn subtract(&self) -> f64 { self.a - self.b } /// Multiplies the two operands. /// /// # Returns /// /// The product of the two operands. pub fn multiply(&self) -> f64 { self.a * self.b } /// Divides the first operand by the second. /// /// # Panics /// /// If the second operand is zero. /// /// # Returns /// /// The quotient of the two operands. pub fn divide(&self) -> f64 { if self.b == 0.0 { panic!("Cannot divide by zero!"); } self.a / self.b } } ``` This code adds documentation comments to the `Calculator` library, explaining its methods and behavior. **Conclusion:** In this lab topic, we wrote tests for a Rust application and documented the code using Rust's documentation features. We created a simple calculator library and wrote tests for its methods, including the division by zero case. We also documented the library using documentation comments, making it easier for others to understand and use our code. **What to Do Next:** * Run the tests using the `cargo test` command. * Generate documentation for the library using the `cargo doc` command. * Experiment with different testing scenarios and documentation comments to improve your understanding of Rust's testing and documentation features. **Additional Resources:** * [The Rust Book: Testing](https://doc.rust-lang.org/book/ch11-01-writing-tests.html) * [The Rust Book: Documentation](https://doc.rust-lang.org/book/ch14-02-publishing-to-crates-io.html) * [Cargo Documentation](https://doc.rust-lang.org/cargo/index.html) **Leave a Comment/Ask for Help:** If you have any questions or need help with this lab topic, leave a comment below.