test: add rETH mock contract

contracts/testing/rETH.vy

@@ -0,0 +1,102 @@
+# @version ^0.2.8
+"""
+@notice Mock rETH token
+@dev This is for testing only, it is NOT safe for use
+"""
+
+from vyper.interfaces import ERC20
+
+interface ERC20Mock:
+    def decimals() -> uint256: view
+    def _mint_for_testing(_target: address, _value: uint256) -> bool: nonpayable
+
+
+event Transfer:
+    _from: indexed(address)
+    _to: indexed(address)
+    _value: uint256
+
+event Approval:
+    _owner: indexed(address)
+    _spender: indexed(address)
+    _value: uint256
+
+
+name: public(String[64])
+symbol: public(String[32])
+decimals: public(uint256)
+balanceOf: public(HashMap[address, uint256])
+allowances: HashMap[address, HashMap[address, uint256]]
+total_supply: uint256
+
+exchangeRateStored: public(uint256)
+
+@external
+def __init__(
+    _name: String[64],
+    _symbol: String[32],
+    _decimals: uint256,
+    _underlying_token: address
+):
+    self.name = _name
+    self.symbol = _symbol
+    self.decimals = _decimals
+    self.exchangeRateStored = 10**18
+
+
+@external
+@view
+def totalSupply() -> uint256:
+    return self.total_supply
+
+
+@external
+@view
+def allowance(_owner : address, _spender : address) -> uint256:
+    return self.allowances[_owner][_spender]
+
+
+@external
+def transfer(_to : address, _value : uint256) -> bool:
+    self.balanceOf[msg.sender] -= _value
+    self.balanceOf[_to] += _value
+    log Transfer(msg.sender, _to, _value)
+    return True
+
+
+@external
+def transferFrom(_from : address, _to : address, _value : uint256) -> bool:
+    self.balanceOf[_from] -= _value
+    self.balanceOf[_to] += _value
+    self.allowances[_from][msg.sender] -= _value
+    log Transfer(_from, _to, _value)
+    return True
+
+
+@external
+def approve(_spender : address, _value : uint256) -> bool:
+    self.allowances[msg.sender][_spender] = _value
+    log Approval(msg.sender, _spender, _value)
+    return True
+
+
+# rETH-specific function
+@view
+@external
+def getExchangeRate() -> uint256:
+    rate: uint256 = self.exchangeRateStored
+    return rate
+
+
+@external
+def set_exchange_rate(rate: uint256): 
+    self.exchangeRateStored = rate
+
+
+@external
+def _mint_for_testing(_target: address, _value: uint256) -> bool:
+    self.total_supply += _value
+    self.balanceOf[_target] += _value
+    log Transfer(ZERO_ADDRESS, _target, _value)
+
+    return True