test(03-01): add 19 unit tests for crypto, compression, and format modules

- crypto: encrypt/decrypt roundtrip, empty data, size formula, HMAC compute/verify, SHA-256 known values
- compression: compress/decompress roundtrip, empty data, large data, should_compress heuristic
- format: header write/read roundtrip, TOC entry roundtrip (ASCII + Cyrillic + empty name), bad magic/version rejection, entry size calculation matching FORMAT.md worked example
- Update hex-literal to v1.1

src/crypto.rs

@@ -76,3 +76,66 @@ pub fn sha256_hash(data: &[u8]) -> [u8; 32] {
     use sha2::Digest;
     sha2::Sha256::digest(data).into()
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::key::KEY;
+    use hex_literal::hex;
+
+    #[test]
+    fn test_encrypt_decrypt_roundtrip() {
+        let plaintext = b"Hello, World!";
+        let iv = [0u8; 16];
+        let ciphertext = encrypt_data(plaintext, &KEY, &iv);
+        let decrypted = decrypt_data(&ciphertext, &KEY, &iv).unwrap();
+        assert_eq!(decrypted, plaintext);
+    }
+
+    #[test]
+    fn test_encrypt_decrypt_empty() {
+        let plaintext = b"";
+        let iv = [0u8; 16];
+        let ciphertext = encrypt_data(plaintext, &KEY, &iv);
+        let decrypted = decrypt_data(&ciphertext, &KEY, &iv).unwrap();
+        assert_eq!(decrypted, plaintext.as_slice());
+    }
+
+    #[test]
+    fn test_encrypted_size_formula() {
+        let iv = [0u8; 16];
+        // 5 bytes -> ((5/16)+1)*16 = 16
+        assert_eq!(encrypt_data(b"Hello", &KEY, &iv).len(), 16);
+        // 16 bytes -> ((16/16)+1)*16 = 32 (full padding block)
+        assert_eq!(encrypt_data(&[0u8; 16], &KEY, &iv).len(), 32);
+        // 0 bytes -> ((0/16)+1)*16 = 16
+        assert_eq!(encrypt_data(b"", &KEY, &iv).len(), 16);
+    }
+
+    #[test]
+    fn test_hmac_compute_verify() {
+        let iv = [0xAA; 16];
+        let ciphertext = b"some ciphertext data here!!12345";
+        let hmac_tag = compute_hmac(&KEY, &iv, ciphertext);
+        // Verify with correct tag
+        assert!(verify_hmac(&KEY, &iv, ciphertext, &hmac_tag));
+        // Verify with wrong tag
+        let wrong_tag = [0u8; 32];
+        assert!(!verify_hmac(&KEY, &iv, ciphertext, &wrong_tag));
+    }
+
+    #[test]
+    fn test_sha256_known_value() {
+        // SHA-256("Hello") from FORMAT.md Section 12.3
+        let expected = hex!("185f8db32271fe25f561a6fc938b2e264306ec304eda518007d1764826381969");
+        let result = sha256_hash(b"Hello");
+        assert_eq!(result, expected);
+    }
+
+    #[test]
+    fn test_sha256_empty() {
+        let expected = hex!("e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855");
+        let result = sha256_hash(b"");
+        assert_eq!(result, expected);
+    }
+}