tools: Ban the usage of ioutil package (#747)

- Resolves #746

We did remove all usage of `ioutil` in: #376
However, over time it has crept back in a few times, this PR will enforce that it stays banned through the linter.

api/http/handler_test.go

@@ -13,7 +13,7 @@ package http
 import (
 	"bytes"
 	"context"
-	"io/ioutil"
+	"io"
 	"math"
 	"net/http"
 	"net/http/httptest"
@@ -141,7 +141,7 @@ func TestSendJSONWithNoErrors(t *testing.T) {
 
 	sendJSON(context.Background(), rec, obj, 200)
 
-	body, err := ioutil.ReadAll(rec.Result().Body)
+	body, err := io.ReadAll(rec.Result().Body)
 	if err != nil {
 		t.Fatal(err)
 	}

config/config_test.go

@@ -12,7 +12,6 @@ package config
 
 import (
 	"encoding/json"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -183,11 +182,16 @@ func TestLoadNonExistingConfigFile(t *testing.T) {
 func TestLoadInvalidConfigFile(t *testing.T) {
 	cfg := DefaultConfig()
 	dir := t.TempDir()
-	ioutil.WriteFile(filepath.Join(dir, DefaultDefraDBConfigFileName), []byte("{"), 0644)
 
-	err := cfg.Load(dir)
+	errWrite := os.WriteFile(
+		filepath.Join(dir, DefaultDefraDBConfigFileName),
+		[]byte("{"),
+		0644,
+	)
+	assert.NoError(t, errWrite)
 
-	assert.Error(t, err)
+	errLoad := cfg.Load(dir)
+	assert.Error(t, errLoad)
 }
 
 func TestInvalidEnvVars(t *testing.T) {
@@ -242,7 +246,6 @@ func TestValidRPCTimeoutDuration(t *testing.T) {
 	_, err := cfg.Net.RPCTimeoutDuration()
 
 	assert.NoError(t, err)
-	assert.NoError(t, err)
 }
 
 func TestInvalidRPCTimeoutDuration(t *testing.T) {

tools/configs/golangci.yaml

@@ -214,6 +214,8 @@ linters-settings:
     # Forbid the following identifiers (identifiers are written using regexp):
     forbid:
       - 'fmt\.Print.*'
+      - 'ioutil\.*'
+
     # Exclude godoc examples from forbidigo checks.
     exclude_godoc_examples: false