Add test for vyperlang#743, ensuring we correctly right pad when a me…

…thod returns.

tests/parser/functions/test_return.py

@@ -0,0 +1,33 @@
+
+def test_correct_abi_right_padding(tester, w3, get_contract_with_gas_estimation):
+    selfcall_code_6 = """
+@public
+def hardtest(arg1: bytes[64], arg2: bytes[64]) -> bytes[128]:
+    return concat(arg1, arg2)
+    """
+
+    c = get_contract_with_gas_estimation(selfcall_code_6)
+
+    assert c.hardtest(b"hello" * 5, b"hello" * 10) == b"hello" * 15
+
+    # Make sure underlying structe is correctly right padded
+    classic_contract = c._classic_contract
+    func = classic_contract.functions.hardtest(b"hello" * 5, b"hello" * 10)
+    tx = func.buildTransaction()
+    del tx['chainId']
+    del tx['gasPrice']
+
+    tx['from'] = w3.eth.accounts[0]
+    res = w3.toBytes(hexstr=tester.call(tx))
+
+    static_offset = int.from_bytes(res[:32], 'big')
+    assert static_offset == 32
+
+    dyn_section = res[static_offset:]
+    assert len(dyn_section) % 32 == 0  # first right pad assert
+
+    len_value = int.from_bytes(dyn_section[:32], 'big')
+
+    assert len_value == len(b"hello" * 15)
+    assert dyn_section[32: 32 + len_value] == b"hello" * 15
+    assert dyn_section[32 + len_value:] == b'\x00' * (len(dyn_section) - 32 - len_value)  # second right pad assert