Instruction length fixes

src/app/emu/memory/memory.h

@@ -270,6 +270,7 @@ class MemoryImpl : public Memory, public Loggable {
     } else {
       // Handle stack underflow
       std::cout << "Stack underflow!" << std::endl;
+      throw std::runtime_error("Stack underflow!");
     }
   }
 
@@ -279,7 +280,7 @@ class MemoryImpl : public Memory, public Loggable {
     } else {
       // Handle stack overflow
       std::cout << "Stack overflow!" << std::endl;
-      return 0;
+      throw std::runtime_error("Stack overflow!");
     }
   }
 

src/app/emu/memory/mock_memory.h

@@ -140,7 +140,7 @@ class MockMemory : public Memory {
           memory_[address + 1] = (value >> 8) & 0xFF;
         });
     ON_CALL(*this, PushByte(::testing::_)).WillByDefault([this](uint8_t value) {
-      memory_.at(SP_) = value;
+      memory_.at(SP_--) = value;
     });
     ON_CALL(*this, PopByte()).WillByDefault([this]() {
       uint8_t value = memory_.at(SP_);
@@ -151,6 +151,7 @@ class MockMemory : public Memory {
         .WillByDefault([this](uint16_t value) {
           memory_.at(SP_) = value & 0xFF;
           memory_.at(SP_ + 1) = (value >> 8) & 0xFF;
+          this->SetSP(SP_ - 2);
         });
     ON_CALL(*this, PopWord()).WillByDefault([this]() {
       uint16_t value = static_cast<uint16_t>(memory_.at(SP_)) |