Consolidate test doubles

- Migrate various mocks of core namespaces to shared version in `fakes` pkg
- Err on the side of making test doubles less sophisticated
- Don't pull over mocks of namespaces that are only used in example code

pkg/core/blockchain.go

@@ -2,7 +2,7 @@ package core
 
 import "math/big"
 
-type Blockchain interface {
+type BlockChain interface {
 	ContractDataFetcher
 	GetBlockByNumber(blockNumber int64) (Block, error)
 	GetHeaderByNumber(blockNumber int64) (Header, error)

pkg/core/eth_client.go

@@ -5,12 +5,15 @@ import (
 	"math/big"
 
 	"github.com/ethereum/go-ethereum"
+	"github.com/ethereum/go-ethereum/common"
 	"github.com/ethereum/go-ethereum/core/types"
 )
 
-type Client interface {
+type EthClient interface {
 	BlockByNumber(ctx context.Context, number *big.Int) (*types.Block, error)
 	CallContract(ctx context.Context, msg ethereum.CallMsg, blockNumber *big.Int) ([]byte, error)
 	FilterLogs(ctx context.Context, q ethereum.FilterQuery) ([]types.Log, error)
 	HeaderByNumber(ctx context.Context, number *big.Int) (*types.Header, error)
+	TransactionSender(ctx context.Context, tx *types.Transaction, block common.Hash, index uint) (common.Address, error)
+	TransactionReceipt(ctx context.Context, txHash common.Hash) (*types.Receipt, error)
 }

pkg/core/rpc_client.go

@@ -0,0 +1,9 @@
+package core
+
+import "context"
+
+type RpcClient interface {
+	CallContext(ctx context.Context, result interface{}, method string, args ...interface{}) error
+	IpcPath() string
+	SupportedModules() (map[string]string, error)
+}