Add subject and test for the exercise `capitalizing`

rust/tests/capitalizing_test/Cargo.lock

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

rust/tests/capitalizing_test/Cargo.toml

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+[package]
+name = "capitalizing_test"
+version = "0.1.0"
+authors = ["MSilva95 <miguel-silva98@hotmail.com>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+capitalizing = { path = "../../../../rust-piscine-solutions/capitalizing"}

rust/tests/capitalizing_test/src/main.rs

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+// Complete the `capitalize_first` function that turns the first letter of a string uppercase.
+// Complete the `title_case` function that turns the first letter of each word in a string uppercase.
+// Complete the `change_case` function that turns the uppercase letters of a string into lowercase and
+// the lowercase letters into uppercase.
+
+use capitalizing::*;
+
+#[allow(dead_code)]
+fn main() {
+	println!("{}", capitalize_first("joe is missing"));
+	println!("{}", title_case("jill is leaving A"));
+	println!("{}", change_case("heLLo THere"));
+}
+
+#[test]
+fn test_success() {
+	assert_eq!(capitalize_first("hello"), "Hello");
+	assert_eq!(capitalize_first("this is working"), "This is working");
+}
+
+#[test]
+fn test_titlle_case() {
+	assert_eq!(title_case("this is a tittle"), "This Is A Tittle");
+	assert_eq!(title_case("hello my name is carl"), "Hello My Name Is Carl");
+}
+
+#[test]
+fn test_change_case() {
+	assert_eq!(change_case("PROgraming"), "proGRAMING");
+	assert_eq!(change_case("heLLo THere"), "HEllO thERE");
+}
+
+#[test]
+fn test_empty() {
+	assert_eq!(capitalize_first(""), "");
+	assert_eq!(title_case(""), "");
+	assert_eq!(change_case(""), "");
+}

subjects/capitalizing/README.md

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+## capitalizing
+
+### Instructions
+
+Complete the `capitalize_first` function that turns the first letter of a string uppercase.
+
+Complete the `title_case` function that turns the first letter of each word in a string uppercase.
+
+Complete the `change_case` function that turns the uppercase letters of a string into lowercase and the lowercase letters into uppercase.
+
+### Expected Functions
+
+```rust
+pub fn capitalize_first(input: &str) -> String {
+}
+
+pub fn title_case(input: &str) -> String {
+}
+
+pub fn change_case(input: &str) -> String {
+}
+```
+
+### Usage
+
+Here is a program to test your function.
+
+```rust
+fn main() {
+    println!("{}", capitalize_first("joe is missing"));
+    println!("{}", title_case("jill is leaving A"));
+    println!("{}",change_case("heLLo THere"));
+}
+```
+
+And its output
+
+```console
+student@ubuntu:~/[[ROOT]]/test$ cargo run
+Joe is missing
+Jill Is Leaving A
+HEllO thERE
+student@ubuntu:~/[[ROOT]]/test$
+```