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/httpserver/server_test.go

@@ -6,7 +6,6 @@ import (
 	"time"
 
 	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
 )
 
 //go:generate mockgen -destination=logger_mock_test.go -package $GOPACKAGE . Logger
@@ -20,11 +19,9 @@ func Test_New(t *testing.T) {
 	testCases := map[string]struct {
 		settings   Settings
 		expected   *Server
-		errWrapped error
 		errMessage string
 	}{
 		"empty settings": {
-			errWrapped: ErrHandlerIsNotSet,
 			errMessage: "http server settings validation failed: HTTP handler cannot be left unset",
 		},
 		"filled settings": {
@@ -52,9 +49,10 @@ func Test_New(t *testing.T) {
 			t.Parallel()
 
 			server, err := New(testCase.settings)
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
-				require.EqualError(t, err, testCase.errMessage)
+			if testCase.errMessage != "" {
+				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 
 			if server != nil {

internal/httpserver/settings.go

@@ -64,14 +64,6 @@ func (s *Settings) OverrideWith(other Settings) {
 	s.ShutdownTimeout = gosettings.OverrideWithComparable(s.ShutdownTimeout, other.ShutdownTimeout)
 }
 
-var (
-	ErrHandlerIsNotSet           = errors.New("HTTP handler cannot be left unset")
-	ErrLoggerIsNotSet            = errors.New("logger cannot be left unset")
-	ErrReadHeaderTimeoutTooSmall = errors.New("read header timeout is too small")
-	ErrReadTimeoutTooSmall       = errors.New("read timeout is too small")
-	ErrShutdownTimeoutTooSmall   = errors.New("shutdown timeout is too small")
-)
-
 func (s Settings) Validate() (err error) {
 	err = validate.ListeningAddress(s.Address, os.Getuid())
 	if err != nil {
@@ -79,31 +71,25 @@ func (s Settings) Validate() (err error) {
 	}
 
 	if s.Handler == nil {
-		return fmt.Errorf("%w", ErrHandlerIsNotSet)
+		return errors.New("HTTP handler cannot be left unset")
 	}
 
 	if s.Logger == nil {
-		return fmt.Errorf("%w", ErrLoggerIsNotSet)
+		return errors.New("logger cannot be left unset")
 	}
 
 	const minReadTimeout = time.Millisecond
 	if s.ReadHeaderTimeout < minReadTimeout {
-		return fmt.Errorf("%w: %s must be at least %s",
-			ErrReadHeaderTimeoutTooSmall,
-			s.ReadHeaderTimeout, minReadTimeout)
+		return fmt.Errorf("read header timeout is too small: %s must be at least %s", s.ReadHeaderTimeout, minReadTimeout)
 	}
 
 	if s.ReadTimeout < minReadTimeout {
-		return fmt.Errorf("%w: %s must be at least %s",
-			ErrReadTimeoutTooSmall,
-			s.ReadTimeout, minReadTimeout)
+		return fmt.Errorf("read timeout is too small: %s must be at least %s", s.ReadTimeout, minReadTimeout)
 	}
 
 	const minShutdownTimeout = 5 * time.Millisecond
 	if s.ShutdownTimeout < minShutdownTimeout {
-		return fmt.Errorf("%w: %s must be at least %s",
-			ErrShutdownTimeoutTooSmall,
-			s.ShutdownTimeout, minShutdownTimeout)
+		return fmt.Errorf("shutdown timeout is too small: %s must be at least %s", s.ShutdownTimeout, minShutdownTimeout)
 	}
 
 	return nil

internal/httpserver/settings_test.go

@@ -5,7 +5,6 @@ import (
 	"testing"
 	"time"
 
-	"github.com/qdm12/gosettings/validate"
 	"github.com/stretchr/testify/assert"
 )
 
@@ -189,30 +188,26 @@ func Test_Settings_Validate(t *testing.T) {
 
 	testCases := map[string]struct {
 		settings   Settings
-		errWrapped error
 		errMessage string
 	}{
 		"bad_address": {
 			settings: Settings{
 				Address: "address:notanint",
 			},
-			errWrapped: validate.ErrPortNotAnInteger,
 			errMessage: "port value is not an integer: notanint",
 		},
 		"nil handler": {
 			settings: Settings{
 				Address: ":8000",
 			},
-			errWrapped: ErrHandlerIsNotSet,
-			errMessage: ErrHandlerIsNotSet.Error(),
+			errMessage: "HTTP handler cannot be left unset",
 		},
 		"nil logger": {
 			settings: Settings{
 				Address: ":8000",
 				Handler: someHandler,
 			},
-			errWrapped: ErrLoggerIsNotSet,
-			errMessage: ErrLoggerIsNotSet.Error(),
+			errMessage: "logger cannot be left unset",
 		},
 		"read header timeout too small": {
 			settings: Settings{
@@ -221,7 +216,6 @@ func Test_Settings_Validate(t *testing.T) {
 				Logger:            someLogger,
 				ReadHeaderTimeout: time.Nanosecond,
 			},
-			errWrapped: ErrReadHeaderTimeoutTooSmall,
 			errMessage: "read header timeout is too small: 1ns must be at least 1ms",
 		},
 		"read timeout too small": {
@@ -232,7 +226,6 @@ func Test_Settings_Validate(t *testing.T) {
 				ReadHeaderTimeout: time.Millisecond,
 				ReadTimeout:       time.Nanosecond,
 			},
-			errWrapped: ErrReadTimeoutTooSmall,
 			errMessage: "read timeout is too small: 1ns must be at least 1ms",
 		},
 		"shutdown timeout too small": {
@@ -244,7 +237,6 @@ func Test_Settings_Validate(t *testing.T) {
 				ReadTimeout:       time.Millisecond,
 				ShutdownTimeout:   time.Millisecond,
 			},
-			errWrapped: ErrShutdownTimeoutTooSmall,
 			errMessage: "shutdown timeout is too small: 1ms must be at least 5ms",
 		},
 		"valid settings": {
@@ -265,9 +257,10 @@ 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)
 			}
 		})
 	}