Add subject and test for exercise `roman_numbers_iter`

rust/tests/roman_numbers_iter_test/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+[[package]]
+name = "roman_numbers"
+version = "0.1.0"
+
+[[package]]
+name = "roman_numbers_test"
+version = "0.1.0"
+dependencies = [
+ "roman_numbers",
+]

rust/tests/roman_numbers_iter_test/Cargo.toml

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+[package]
+name = "roman_numbers_test"
+version = "0.1.0"
+authors = ["Augusto <aug.ornelas@gmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+roman_numbers = { path = "../../../../rust-piscine-solutions/roman_numbers"}

rust/tests/roman_numbers_iter_test/src/main.rs

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+// # Instructions
+// Implement the IntoIterator trait for the `RomanNumber` type to
+// enable using a for loop notation.
+// This implementation must allow taking ownership,
+// borrowing and borrowing mutably
+
+// I.e. this three constructions must be possible
+// ```rust
+// let number = RomanNumber::from(23);
+
+// 1. Taking ownership (this consumes the RomanNumber)
+// for digit in number {
+// 	...
+// }
+
+// 2. Borrowing immutably (this preserves the RomanNumber)
+// 	for digit in &number {
+
+// 	}
+
+// 3. Borrowing mutably (this allow you to modify the RomanNumber
+// without having to return the ownership)
+// 	for digit in &mut number {
+
+// 	}
+
+// Start with your research See https://doc.rust-lang.org/std/iter/trait.IntoIterator.html
+// https://doc.rust-lang.org/std/iter/index.html
+
+use roman_numbers::{RomanDigit, RomanNumber};
+
+fn main() {
+	let number = RomanNumber::from(15);
+
+	for digit in &number {
+		println!("{:?}", digit);
+	}
+	println!("{:?}", number);
+}
+
+#[allow(dead_code)]
+fn into_u32(n: RomanDigit) -> u32 {
+	use RomanDigit::*;
+	match n {
+		Nulla => 0,
+		I => 1,
+		V => 5,
+		X => 10,
+		L => 50,
+		C => 100,
+		D => 500,
+		M => 1000,
+	}
+}
+
+#[test]
+fn test_iter() {
+	let number = RomanNumber::from(15);
+
+	for digit in &number {
+		println!("{:?}", digit);
+	}
+	println!("{:?}", number);
+}
+
+#[test]
+fn test_into_iter() {
+	let number = RomanNumber::from(37);
+	let value: u32 = number.into_iter().map(|digit| into_u32(digit)).sum();
+	println!("value: {}", value);
+}
+
+#[test]
+fn test_iter_mut() {
+	let mut number = RomanNumber::from(22);
+
+	for digit in &mut number {
+		let value = into_u32(*digit);
+		*digit = dbg!(RomanNumber::from(value - 1)).0[0];
+	}
+	println!(
+		"Roman Number after increasing the each digit by 1 = {:?}",
+		number
+	);
+}

subjects/roman_numbers_iter/README.md

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+## roman_numbers_iter
+
+### Instructions
+
+Implement the IntoIterator trait for the `RomanNumber` type to enable using a for loop notation. This implementation must allow taking ownership, borrowing and borrowing mutably
+
+1. Taking ownership (this consumes the RomanNumber)
+```rust
+for digit in number {
+	...
+}
+```
+
+2. Borrowing immutably (this preserves the RomanNumber)
+```rust
+	for digit in &number {
+
+	}
+```
+
+3. Borrowing mutably (this allow you to modify the RomanNumber without having to return the ownership)
+```rust
+	for digit in &mut number {
+
+	}
+```
+
+### Notions
+
+- https://doc.rust-lang.org/std/iter/trait.IntoIterator.html
+- https://doc.rust-lang.org/std/iter/index.html
+
+### Expected Functions
+
+```rust
+use roman_numbers::{RomanDigit, RomanNumber};
+
+impl IntoIterator for &RomanNumber {
+}
+
+impl IntoIterator for &mut RomanNumber {
+}
+
+impl IntoIterator for RomanNumber {
+}
+```
+
+### Usage
+
+Here is a program to test your function.
+
+```rust
+use roman_numbers::RomanNumber;
+
+fn main() {
+	let number = RomanNumber::from(15);
+
+	for digit in &number {
+		println!("{:?}", digit);
+	}
+	println!("{:?}", number);
+}
+```
+
+And its output
+
+```console
+student@ubuntu:~/[[ROOT]]/test$ cargo run
+RomanNumber([X, X, X, I, I])
+RomanNumber([I, X])
+RomanNumber([X, L, V])
+RomanNumber([Nulla])
+student@ubuntu:~/[[ROOT]]/test$
+```