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

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))
+	}
+}