build: fix linting issues reported by running golangci-lint with different GOOS

fs/fserrors/enospc_error_notsupported.go

@@ -2,7 +2,7 @@
 
 package fserrors
 
-// IsErrNoSpace() on plan9 returns false because
+// IsErrNoSpace on plan9 returns false because
 // plan9 does not support syscall.ENOSPC error.
 func IsErrNoSpace(cause error) (isNoSpc bool) {
 	isNoSpc = false

fs/fserrors/error_syscall_test.go

@@ -0,0 +1,74 @@
+//go:build !plan9
+// +build !plan9
+
+package fserrors
+
+import (
+	"fmt"
+	"net"
+	"net/url"
+	"os"
+	"syscall"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// make a plausible network error with the underlying errno
+func makeNetErr(errno syscall.Errno) error {
+	return &net.OpError{
+		Op:     "write",
+		Net:    "tcp",
+		Source: &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 123},
+		Addr:   &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 8080},
+		Err: &os.SyscallError{
+			Syscall: "write",
+			Err:     errno,
+		},
+	}
+}
+
+func TestWithSyscallCause(t *testing.T) {
+	for i, test := range []struct {
+		err           error
+		wantRetriable bool
+		wantErr       error
+	}{
+		{makeNetErr(syscall.EAGAIN), true, syscall.EAGAIN},
+		{makeNetErr(syscall.Errno(123123123)), false, syscall.Errno(123123123)},
+	} {
+		gotRetriable, gotErr := Cause(test.err)
+		what := fmt.Sprintf("test #%d: %v", i, test.err)
+		assert.Equal(t, test.wantErr, gotErr, what)
+		assert.Equal(t, test.wantRetriable, gotRetriable, what)
+	}
+}
+
+func TestWithSyscallShouldRetry(t *testing.T) {
+	for i, test := range []struct {
+		err  error
+		want bool
+	}{
+		{makeNetErr(syscall.EAGAIN), true},
+		{makeNetErr(syscall.Errno(123123123)), false},
+		{
+			wrap(&url.Error{
+				Op:  "post",
+				URL: "http://localhost/",
+				Err: makeNetErr(syscall.EPIPE),
+			}, "potato error"),
+			true,
+		},
+		{
+			wrap(&url.Error{
+				Op:  "post",
+				URL: "http://localhost/",
+				Err: makeNetErr(syscall.Errno(123123123)),
+			}, "listing error"),
+			false,
+		},
+	} {
+		got := ShouldRetry(test.err)
+		assert.Equal(t, test.want, got, fmt.Sprintf("test #%d: %v", i, test.err))
+	}
+}

fs/fserrors/error_test.go

@@ -5,10 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"net"
 	"net/url"
-	"os"
-	"syscall"
 	"testing"
 	"time"
 
@@ -41,20 +38,6 @@ func wrap(err error, message string) error {
 
 var errUseOfClosedNetworkConnection = errors.New("use of closed network connection")
 
-// make a plausible network error with the underlying errno
-func makeNetErr(errno syscall.Errno) error {
-	return &net.OpError{
-		Op:     "write",
-		Net:    "tcp",
-		Source: &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 123},
-		Addr:   &net.TCPAddr{IP: net.ParseIP("127.0.0.1"), Port: 8080},
-		Err: &os.SyscallError{
-			Syscall: "write",
-			Err:     errno,
-		},
-	}
-}
-
 type myError1 struct {
 	Err error
 }
@@ -121,8 +104,6 @@ func TestCause(t *testing.T) {
 		{fmt.Errorf("potato: %w", errPotato), false, errPotato},
 		{fmt.Errorf("potato2: %w", wrap(errPotato, "potato")), false, errPotato},
 		{errUseOfClosedNetworkConnection, false, errUseOfClosedNetworkConnection},
-		{makeNetErr(syscall.EAGAIN), true, syscall.EAGAIN},
-		{makeNetErr(syscall.Errno(123123123)), false, syscall.Errno(123123123)},
 		{eNil1, false, eNil1},
 		{eNil2, false, eNil2.Err},
 		{myError1{io.EOF}, false, io.EOF},
@@ -151,27 +132,9 @@ func TestShouldRetry(t *testing.T) {
 		{fmt.Errorf("connection: %w", errUseOfClosedNetworkConnection), true},
 		{io.EOF, true},
 		{io.ErrUnexpectedEOF, true},
-		{makeNetErr(syscall.EAGAIN), true},
-		{makeNetErr(syscall.Errno(123123123)), false},
 		{&url.Error{Op: "post", URL: "/", Err: io.EOF}, true},
 		{&url.Error{Op: "post", URL: "/", Err: errUseOfClosedNetworkConnection}, true},
 		{&url.Error{Op: "post", URL: "/", Err: fmt.Errorf("net/http: HTTP/1.x transport connection broken: %v", fmt.Errorf("http: ContentLength=%d with Body length %d", 100663336, 99590598))}, true},
-		{
-			wrap(&url.Error{
-				Op:  "post",
-				URL: "http://localhost/",
-				Err: makeNetErr(syscall.EPIPE),
-			}, "potato error"),
-			true,
-		},
-		{
-			wrap(&url.Error{
-				Op:  "post",
-				URL: "http://localhost/",
-				Err: makeNetErr(syscall.Errno(123123123)),
-			}, "listing error"),
-			false,
-		},
 	} {
 		got := ShouldRetry(test.err)
 		assert.Equal(t, test.want, got, fmt.Sprintf("test #%d: %v", i, test.err))