tests - Add test for JR e instruction

tests/test_cpu_simple.cpp

@@ -172,3 +172,25 @@ TEST_CASE("CALL ; RET")
   CHECK(cpu.state.PC == 0x0006);
   CHECK(cpu.state.SP == 0x0010);
 }
+
+TEST_CASE("JR e")
+{
+  u8 test_ram[] = {
+    0x18, 0x02,
+    0x00, 0x00,
+    0x18, (u8)(-0x06),
+  };
+
+  RAM r(test_ram, 0x6, true);
+  Cpu cpu(&r);
+
+  CHECK(cpu.state.PC == 0x0);
+
+  cpu.step();
+
+  CHECK(cpu.state.PC == 0x4);
+
+  cpu.step();
+
+  CHECK(cpu.state.PC == 0x0);
+}