Add test for tx validation in tx pool

tests/trinity/plugins/tx_pool/test_default_transaction_validator.py

@@ -0,0 +1,63 @@
+import pytest
+
+from eth.chains.base import (
+    MiningChain,
+)
+from eth.tools.builder.chain import api
+from eth.vm.forks.frontier.transactions import (
+    FrontierTransaction,
+)
+from eth.vm.forks.homestead.transactions import (
+    HomesteadTransaction,
+)
+from eth.vm.forks.spurious_dragon.transactions import (
+    SpuriousDragonTransaction,
+)
+
+from trinity.plugins.builtin.tx_pool.validators import (
+    DefaultTransactionValidator,
+)
+
+
+@pytest.mark.parametrize(
+    (
+        'initial_block_number',
+        'expected_initial_tx_class',
+        'expected_outdated_tx_class',
+        'expected_future_tx_class',
+    ),
+    [
+        (1, FrontierTransaction, None, SpuriousDragonTransaction,),
+        (5, HomesteadTransaction, FrontierTransaction, SpuriousDragonTransaction,),
+        (6, HomesteadTransaction, FrontierTransaction, SpuriousDragonTransaction,),
+        # If no initial block number is specified, the latest VM is assumed to be active
+        (None, SpuriousDragonTransaction, HomesteadTransaction, SpuriousDragonTransaction,),
+    ],
+)
+def test_tx_class_resolution(initial_block_number,
+                             expected_initial_tx_class,
+                             expected_outdated_tx_class,
+                             expected_future_tx_class):
+    chain = api.build(
+        MiningChain,
+        api.frontier_at(0),
+        api.homestead_at(5),
+        api.spurious_dragon_at(10),
+        api.disable_pow_check,
+        api.genesis
+    )
+    validator = DefaultTransactionValidator(chain, initial_block_number)
+    assert validator.get_appropriate_tx_class() == expected_initial_tx_class
+
+    if expected_outdated_tx_class is not None:
+        assert validator.is_outdated_tx_class(expected_outdated_tx_class)
+
+    # The `get_appropriate_tx_class` method has a cache decorator applied
+    # To test it properly, we need to clear the cache
+    validator.get_appropriate_tx_class.cache_clear()
+
+    # Check that the validator uses the correct tx class when we have reached the tip of the chain
+    for n in range(10):
+        chain.mine_block()
+
+    assert validator.get_appropriate_tx_class() == expected_future_tx_class