chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/pprof/server_test.go

@@ -120,7 +120,7 @@ func Test_Server_BadSettings(t *testing.T) {
 
 	server, err := New(settings)
 	assert.Nil(t, server)
-	assert.ErrorIs(t, err, ErrBlockProfileRateNegative)
+	assert.ErrorContains(t, err, "block profile rate cannot be negative")
 	const expectedErrMessage = "pprof settings failed validation: block profile rate cannot be negative"
 	assert.EqualError(t, err, expectedErrMessage)
 }

internal/pprof/settings.go

@@ -2,7 +2,6 @@ package pprof
 
 import (
 	"errors"
-	"fmt"
 	"time"
 
 	"github.com/qdm12/gluetun/internal/httpserver"
@@ -51,18 +50,13 @@ func (s *Settings) OverrideWith(other Settings) {
 	s.HTTPServer.OverrideWith(other.HTTPServer)
 }
 
-var (
-	ErrBlockProfileRateNegative = errors.New("block profile rate cannot be negative")
-	ErrMutexProfileRateNegative = errors.New("mutex profile rate cannot be negative")
-)
-
 func (s Settings) Validate() (err error) {
 	if *s.BlockProfileRate < 0 {
-		return fmt.Errorf("%w", ErrBlockProfileRateNegative)
+		return errors.New("block profile rate cannot be negative")
 	}
 
 	if *s.MutexProfileRate < 0 {
-		return fmt.Errorf("%w", ErrMutexProfileRateNegative)
+		return errors.New("mutex profile rate cannot be negative")
 	}
 
 	return s.HTTPServer.Validate()

internal/pprof/settings_test.go

@@ -6,7 +6,6 @@ import (
 	"time"
 
 	"github.com/qdm12/gluetun/internal/httpserver"
-	"github.com/qdm12/gosettings/validate"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -195,7 +194,6 @@ func Test_Settings_Validate(t *testing.T) {
 
 	testCases := map[string]struct {
 		settings   Settings
-		errWrapped error
 		errMessage string
 	}{
 		"negative block profile rate": {
@@ -203,16 +201,14 @@ func Test_Settings_Validate(t *testing.T) {
 				BlockProfileRate: intPtr(-1),
 				MutexProfileRate: intPtr(0),
 			},
-			errWrapped: ErrBlockProfileRateNegative,
-			errMessage: ErrBlockProfileRateNegative.Error(),
+			errMessage: "block profile rate cannot be negative",
 		},
 		"negative mutex profile rate": {
 			settings: Settings{
 				BlockProfileRate: intPtr(0),
 				MutexProfileRate: intPtr(-1),
 			},
-			errWrapped: ErrMutexProfileRateNegative,
-			errMessage: ErrMutexProfileRateNegative.Error(),
+			errMessage: "mutex profile rate cannot be negative",
 		},
 		"http server validation error": {
 			settings: Settings{
@@ -222,7 +218,6 @@ func Test_Settings_Validate(t *testing.T) {
 					Address: ":x",
 				},
 			},
-			errWrapped: validate.ErrPortNotAnInteger,
 			errMessage: "port value is not an integer: x",
 		},
 		"valid settings": {
@@ -247,9 +242,10 @@ func Test_Settings_Validate(t *testing.T) {
 
 			err := testCase.settings.Validate()
 
-			assert.ErrorIs(t, err, testCase.errWrapped)
 			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 		})
 	}