diff --git a/src/emu.rs b/src/emu.rs
index 696c721..8e50f47 100644
--- a/src/emu.rs
+++ b/src/emu.rs
@@ -236,8 +236,7 @@ impl Chip8 {
 
     fn add_vx_byte(&mut self, x: u8, kk: u8) {
         // calculate Vx + kk, then store it in Vx
-        let x = x as usize;
-        self.v[x] = self.v[x] + kk;
+        self.v[x as usize] += kk;
     }
 
     fn ld_vx_vy(&mut self, x: u8, y: u8) {
@@ -247,8 +246,7 @@ impl Chip8 {
 
     fn or(&mut self, x: u8, y: u8) {
         // calc bitwise OR on Vx and Vy, then store in Vx
-        let x = x as usize;
-        self.v[x] = self.v[x] | self.v[y as usize];
+        self.v[x as usize] |= self.v[y as usize];
     }
 
     fn and_vx_vy(&mut self, x: u8, y: u8) {
@@ -259,8 +257,7 @@ impl Chip8 {
 
     fn xor(&mut self, x: u8, y: u8) {
         // calc bitwise XOR on Vx and Vy, then store in Vx
-        let x = x as usize;
-        self.v[x] = self.v[x] ^ self.v[y as usize];
+        self.v[x as usize] ^= self.v[y as usize];
     }
 
     fn add_vx_vy(&mut self, x: u8, y: u8) {
@@ -552,4 +549,177 @@ mod test {
         assert_eq!(chip8.sp, 0);
         assert_eq!(chip8.pc, 0x50D5);
     }
+
+    #[test]
+    fn opcode_jmp_addr_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        let opcode = 0x1ABC;
+        let nnn = opcode & 0x0FFF;
+
+        chip8.jmp_addr(nnn);
+
+        assert_eq!(chip8.pc, nnn);
+    }
+
+    #[test]
+    fn opcode_call_addr_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        let nnn = 0x0ABC;
+        chip8.call_addr(nnn);
+
+        assert_eq!(chip8.sp, 1);
+        assert_eq!(chip8.stack[chip8.sp as usize], 0x200);
+        assert_eq!(chip8.pc, nnn);
+    }
+
+    #[test]
+    fn opcode_se_vx_byte_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        // Opcode: 0x32D5
+
+        // Test Vx == kk
+        chip8.pc = 0x200;
+        chip8.v[2] = 0xD5;
+        chip8.se_vx_byte(0x2, 0xD5);
+
+        assert_eq!(chip8.pc, 0x202);
+
+        // Test Vx != kk
+        chip8.pc = 0x200;
+        chip8.v[2] = 0xD6;
+        chip8.se_vx_byte(0x2, 0xD5);
+
+        assert_ne!(chip8.pc, 0x202);
+    }
+
+    #[test]
+    fn opcode_sne_vx_byte_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        // Opcode: 0x32D6
+
+        // Test Vx != kk
+        chip8.pc = 0x200;
+        chip8.v[2] = 0xD5;
+        chip8.sne_vx_byte(0x2, 0xD6);
+
+        assert_eq!(chip8.pc, 0x202);
+
+        // Test Vx == kk
+        chip8.pc = 0x200;
+        chip8.v[2] = 0xD6;
+        chip8.sne_vx_byte(0x2, 0xD6);
+
+        assert_ne!(chip8.pc, 0x202);
+    }
+
+    #[test]
+    fn opcode_se_vx_vy_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        // When Equal
+        chip8.pc = 0x200;
+        chip8.v[4] = 0xAB;
+        chip8.v[7] = 0xAB;
+        chip8.se_vx_vy(0x4, 0x7);
+
+        assert_eq!(chip8.pc, 0x202);
+
+        // When not Equal
+        chip8.pc = 0x200;
+        chip8.v[4] = 0xAC;
+        chip8.v[7] = 0xAB;
+
+        chip8.se_vx_vy(0x4, 0x7);
+        assert_eq!(chip8.pc, 0x200);
+    }
+
+    #[test]
+    fn opcode_ld_vx_byte_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        assert_ne!(chip8.v[5], 0xAB);
+        chip8.ld_vx_byte(0x5, 0xAB);
+        assert_eq!(chip8.v[5], 0xAB);
+    }
+
+    #[test]
+    fn opcode_add_vx_byte_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        chip8.v[3] = 0x0A;
+        chip8.add_vx_byte(0x3, 0x36);
+        assert_eq!(chip8.v[3], 0x40);
+    }
+
+    #[test]
+    fn opcode_ld_vx_vy_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        chip8.v[1] = 0x64;
+        chip8.v[4] = 0x96;
+
+        chip8.ld_vx_vy(0x1, 0x4);
+        assert_eq!(chip8.v[1], 0x96);
+    }
+
+    #[test]
+    fn opcode_or_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        chip8.v[0xA] = 0xAB;
+        chip8.v[0x9] = 0xC6;
+
+        chip8.or(0xA, 0x9);
+        assert_eq!(chip8.v[0xA], 0xAB | 0xC6);
+    }
+
+    #[test]
+    fn opcode_and_vx_vy_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        chip8.v[0xC] = 0x58;
+        chip8.v[0x2] = 0x9a;
+
+        chip8.and_vx_vy(0xC, 0x2);
+        assert_eq!(chip8.v[0xC], 0x58 & 0x9a);
+    }
+
+    #[test]
+    fn opcode_xor_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        chip8.v[0x5] = 0x38;
+        chip8.v[0xB] = 0x4C;
+
+        chip8.xor(0x5, 0xB);
+        assert_eq!(chip8.v[0x5], 0x38 ^ 0x4C);
+    }
+
+    #[test]
+    fn opcode_add_vx_vy_works() {
+        let mut chip8: Chip8 = Default::default();
+
+        chip8.v[0xA] = 0x01;
+        chip8.v[0x8] = 0xC8;
+
+        chip8.add_vx_vy(0xA, 0x8);
+        assert_eq!(chip8.v[0xA], 0x01 + 0xC8);
+    }
+
+    #[test]
+    fn opcode_add_vx_vy_overflows_as_expected() {
+        let mut chip8: Chip8 = Default::default();
+
+        chip8.v[0xE] = 0xFF;
+        chip8.v[0x7] = 0x01;
+
+        chip8.add_vx_vy(0xE, 0x7);
+
+        assert_eq!(chip8.v[0xA], (0xFF as u8).wrapping_add(0x01));
+        assert_eq!(chip8.v[0xF], 1);
+    }
 }