diff --git a/cli/smartcontract/smart_contract.go b/cli/smartcontract/smart_contract.go
index 4cd604e59..be9b1cbd9 100644
--- a/cli/smartcontract/smart_contract.go
+++ b/cli/smartcontract/smart_contract.go
@@ -18,8 +18,8 @@ import (
 )
 
 var (
-	errNoInput             = errors.New("No input file was found, specify an input file with the '--in or -i' flag")
-	errNoSmartContractName = errors.New("No name was provided, specify the '--name or -n' flag")
+	errNoInput             = errors.New("no input file was found, specify an input file with the '--in or -i' flag")
+	errNoSmartContractName = errors.New("no name was provided, specify the '--name or -n' flag")
 	errFileExist           = errors.New("A file with given smart-contract name already exists")
 )
 
diff --git a/pkg/core/block_test.go b/pkg/core/block_test.go
index 1c2f5e790..b56a7ec36 100644
--- a/pkg/core/block_test.go
+++ b/pkg/core/block_test.go
@@ -164,7 +164,7 @@ func TestBinBlockDecodeEncode(t *testing.T) {
 		"908a398dd65dfd2aad6c06090c5a71d5e5280746577a6ddd5a1f2c1453f71ead": false,
 	}
 
-	hashes := []string{}
+	var hashes []string
 
 	for _, tx := range b.Transactions {
 		switch tx.Type {
diff --git a/pkg/core/transaction/contract_test.go b/pkg/core/transaction/contract_test.go
index 6d6ed4ef0..28bc42032 100644
--- a/pkg/core/transaction/contract_test.go
+++ b/pkg/core/transaction/contract_test.go
@@ -17,7 +17,7 @@ func TestEncodeDecodeContract(t *testing.T) {
 	assert.Equal(t, ContractType, tx.Type)
 	assert.IsType(t, tx.Data, &ContractTX{})
 	assert.Equal(t, 0, int(tx.Version))
-	assert.Equal(t, 1, int(len(tx.Inputs)))
+	assert.Equal(t, 1, len(tx.Inputs))
 
 	input := tx.Inputs[0]
 
diff --git a/pkg/core/unspent_coin_state.go b/pkg/core/unspent_coin_state.go
index ab9cabfaa..a7b566fd8 100644
--- a/pkg/core/unspent_coin_state.go
+++ b/pkg/core/unspent_coin_state.go
@@ -122,15 +122,14 @@ func IsDoubleSpend(s storage.Store, tx *transaction.Transaction) bool {
 			if r.Err != nil {
 				return false
 			}
-			if unspent == nil {
-				return true
-			}
 
 			for _, input := range inputs {
 				if int(input.PrevIndex) >= len(unspent.states) || unspent.states[input.PrevIndex] == CoinStateSpent {
 					return true
 				}
 			}
+		} else {
+			return true
 		}
 
 	}
diff --git a/pkg/smartcontract/contract_test.go b/pkg/smartcontract/contract_test.go
index 1cca3d229..d011aa1b7 100644
--- a/pkg/smartcontract/contract_test.go
+++ b/pkg/smartcontract/contract_test.go
@@ -28,7 +28,7 @@ func TestCreateMultiSigRedeemScript(t *testing.T) {
 
 	for i := 0; i < len(validators); i++ {
 		bb := br.ReadBytes()
-		if err != nil {
+		if br.Err != nil {
 			t.Fatal(err)
 		}
 		assert.Equal(t, validators[i].Bytes(), bb)
diff --git a/pkg/util/fixed8.go b/pkg/util/fixed8.go
index 1364a0601..f28f74e45 100644
--- a/pkg/util/fixed8.go
+++ b/pkg/util/fixed8.go
@@ -12,7 +12,7 @@ const (
 	decimals  = 100000000
 )
 
-var errInvalidString = errors.New("Fixed8 must satisfy following regex \\d+(\\.\\d{1,8})?")
+var errInvalidString = errors.New("fixed8 must satisfy following regex \\d+(\\.\\d{1,8})?")
 
 // Fixed8 represents a fixed-point number with precision 10^-8.
 type Fixed8 int64
diff --git a/pkg/vm/cli/cli.go b/pkg/vm/cli/cli.go
index f871db287..d5f4461f4 100644
--- a/pkg/vm/cli/cli.go
+++ b/pkg/vm/cli/cli.go
@@ -213,7 +213,7 @@ func handleBreak(c *ishell.Context) {
 	}
 	v := getVMFromContext(c)
 	if len(c.Args) != 1 {
-		c.Err(errors.New("Missing parameter <ip>"))
+		c.Err(errors.New("missing parameter <ip>"))
 	}
 	n, err := strconv.Atoi(c.Args[0])
 	if err != nil {
diff --git a/pkg/vm/compiler/compiler.go b/pkg/vm/compiler/compiler.go
index 94bf31ee8..1bb1cc9b8 100644
--- a/pkg/vm/compiler/compiler.go
+++ b/pkg/vm/compiler/compiler.go
@@ -87,7 +87,7 @@ func CompileAndSave(src string, o *Options) error {
 	}
 	b, err = Compile(bytes.NewReader(b), o)
 	if err != nil {
-		return fmt.Errorf("Error while trying to compile smart contract file: %v", err)
+		return fmt.Errorf("error while trying to compile smart contract file: %v", err)
 	}
 
 	log.Println(hex.EncodeToString(b))
diff --git a/pkg/vm/compiler/emit.go b/pkg/vm/compiler/emit.go
index 584979e5d..92be632f8 100644
--- a/pkg/vm/compiler/emit.go
+++ b/pkg/vm/compiler/emit.go
@@ -85,7 +85,7 @@ func emitSyscall(w *bytes.Buffer, api string) error {
 	}
 	buf := make([]byte, len(api)+1)
 	buf[0] = byte(len(api))
-	copy(buf[1:], []byte(api))
+	copy(buf[1:], api)
 	return emit(w, vm.SYSCALL, buf)
 }
 
diff --git a/pkg/vm/emit.go b/pkg/vm/emit.go
index 14556b039..db76fc238 100644
--- a/pkg/vm/emit.go
+++ b/pkg/vm/emit.go
@@ -91,7 +91,7 @@ func EmitSyscall(w *bytes.Buffer, api string) error {
 	}
 	buf := make([]byte, len(api)+1)
 	buf[0] = byte(len(api))
-	copy(buf[1:], []byte(api))
+	copy(buf[1:], api)
 	return Emit(w, SYSCALL, buf)
 }
 
diff --git a/pkg/vm/stack_item.go b/pkg/vm/stack_item.go
index 468453d7b..925676a67 100644
--- a/pkg/vm/stack_item.go
+++ b/pkg/vm/stack_item.go
@@ -67,7 +67,7 @@ func makeStackItem(v interface{}) StackItem {
 	case StackItem:
 		return val
 	case []int:
-		a := []StackItem{}
+		var a []StackItem
 		for _, i := range val {
 			a = append(a, makeStackItem(i))
 		}
diff --git a/pkg/vm/tests/assign_test.go b/pkg/vm/tests/assign_test.go
index 5c2460d41..7882048ec 100644
--- a/pkg/vm/tests/assign_test.go
+++ b/pkg/vm/tests/assign_test.go
@@ -131,5 +131,5 @@ var assignTestCases = []testCase{
 }
 
 func TestAssignments(t *testing.T) {
-	run_testcases(t, assignTestCases)
+	runTestCases(t, assignTestCases)
 }
diff --git a/pkg/vm/tests/binary_expr_test.go b/pkg/vm/tests/binary_expr_test.go
index fd24c2e37..257132bff 100644
--- a/pkg/vm/tests/binary_expr_test.go
+++ b/pkg/vm/tests/binary_expr_test.go
@@ -189,5 +189,5 @@ var binaryExprTestCases = []testCase{
 }
 
 func TestBinaryExprs(t *testing.T) {
-	run_testcases(t, binaryExprTestCases)
+	runTestCases(t, binaryExprTestCases)
 }
diff --git a/pkg/vm/tests/numeric_test.go b/pkg/vm/tests/numeric_test.go
index 53fc3e722..d2589dbf5 100644
--- a/pkg/vm/tests/numeric_test.go
+++ b/pkg/vm/tests/numeric_test.go
@@ -21,5 +21,5 @@ var numericTestCases = []testCase{
 }
 
 func TestNumericExprs(t *testing.T) {
-	run_testcases(t, numericTestCases)
+	runTestCases(t, numericTestCases)
 }
diff --git a/pkg/vm/tests/struct_test.go b/pkg/vm/tests/struct_test.go
index e3de28f91..d739a935f 100644
--- a/pkg/vm/tests/struct_test.go
+++ b/pkg/vm/tests/struct_test.go
@@ -240,5 +240,5 @@ var structTestCases = []testCase{
 }
 
 func TestStructs(t *testing.T) {
-	run_testcases(t, structTestCases)
+	runTestCases(t, structTestCases)
 }
diff --git a/pkg/vm/tests/vm_test.go b/pkg/vm/tests/vm_test.go
index 885e3ebc6..b91b8bb75 100644
--- a/pkg/vm/tests/vm_test.go
+++ b/pkg/vm/tests/vm_test.go
@@ -16,7 +16,7 @@ type testCase struct {
 	result interface{}
 }
 
-func run_testcases(t *testing.T, tcases []testCase) {
+func runTestCases(t *testing.T, tcases []testCase) {
 	for _, tcase := range tcases {
 		t.Run(tcase.name, func(t *testing.T) { eval(t, tcase.src, tcase.result) })
 	}