fix: make gas estimation test reproducible (#890)

Closes: #536

Solution: Use a fixed test account.

The source of non-deterministic is tx's intrinsic gas is different according to different number of zeros in input data,
so to make sure the gas number is reproducible, and the randomly generated test address is included in that.

x/evm/keeper/keeper_test.go

@@ -72,9 +72,12 @@ type KeeperTestSuite struct {
 func (suite *KeeperTestSuite) DoSetupTest(t require.TestingT) {
 	checkTx := false
 
-	// account key
-	priv, err := ethsecp256k1.GenerateKey()
+	// account key, use a constant account to keep unit test deterministic.
+	ecdsaPriv, err := crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291")
 	require.NoError(t, err)
+	priv := &ethsecp256k1.PrivKey{
+		Key: crypto.FromECDSA(ecdsaPriv),
+	}
 	suite.address = common.BytesToAddress(priv.PubKey().Address().Bytes())
 	suite.signer = tests.NewSigner(priv)