Add tests for extcodecopy (#1240)

* Add tests for extcodecopy

* Don't use mock

tests/instructions/extcodecopy_test.py

@@ -0,0 +1,57 @@
+from mythril.laser.smt import symbol_factory
+from mythril.disassembler.disassembly import Disassembly
+from mythril.laser.ethereum.state.environment import Environment
+from mythril.laser.ethereum.state.machine_state import MachineState
+from mythril.laser.ethereum.state.global_state import GlobalState
+from mythril.laser.ethereum.state.world_state import WorldState
+from mythril.laser.ethereum.instructions import Instruction
+from mythril.laser.ethereum.transaction.transaction_models import MessageCallTransaction
+
+
+def test_extcodecopy():
+    # Arrange
+    new_world_state = WorldState()
+    new_account = new_world_state.create_account(balance=10, address=101)
+    new_account.code = Disassembly("60616240")
+    ext_account = new_world_state.create_account(balance=1000, address=121)
+    ext_account.code = Disassembly("6040404040")
+
+    new_environment = Environment(new_account, None, None, None, None, None)
+    state = GlobalState(
+        new_world_state, new_environment, None, MachineState(gas_limit=8000000)
+    )
+    state.transaction_stack.append(
+        (MessageCallTransaction(world_state=WorldState(), gas_limit=8000000), None)
+    )
+
+    state.mstate.stack = [3, 0, 0, 121]
+    instruction = Instruction("extcodecopy", dynamic_loader=None)
+
+    # Act
+    new_state = instruction.evaluate(state)[0]
+    # Assert
+    assert new_state.mstate.memory[0:3] == [96, 64, 64]
+
+
+def test_extcodecopy_fail():
+    # Arrange
+    new_world_state = WorldState()
+    new_account = new_world_state.create_account(balance=10, address=101)
+    new_account.code = Disassembly("60616240")
+    new_environment = Environment(new_account, None, None, None, None, None)
+    state = GlobalState(
+        new_world_state, new_environment, None, MachineState(gas_limit=8000000)
+    )
+    state.transaction_stack.append(
+        (MessageCallTransaction(world_state=WorldState(), gas_limit=8000000), None)
+    )
+
+    state.mstate.stack = [2, 2, 2, symbol_factory.BitVecSym("FAIL", 256)]
+    instruction = Instruction("extcodecopy", dynamic_loader=None)
+
+    # Act
+    new_state = instruction.evaluate(state)[0]
+
+    # Assert
+    assert new_state.mstate.stack == []
+    assert new_state.mstate.memory._memory == state.mstate.memory._memory