I am trying to learn how to write tests for my code in order to write better code, but I just seem to have the hardest time figuring out how to actually test some code I have written. I have read so many tutorials, most of which seem to only cover functions that add two numbers or mock some database or server.
I have a simple function I wrote below that takes a text template and a CSV file as input and executes the template using the values of the CSV. I have "tested" the code by trial and error, passing files, and printing values, but I would like to learn how to write proper tests for it. I feel that learning to test my own code will help me understand and learn faster and better. Any help is appreciated.
// generateCmds generates configuration commands from a text template using
// the values from a CSV file. Multiple commands in the text template must
// be delimited by a semicolon. The first row of the CSV file is assumed to
// be the header row and the header values are used for key access in the
// text template.
func generateCmds(cmdTmpl string, filename string) ([]string, error) {
t, err := template.New("cmds").Parse(cmdTmpl)
if err != nil {
return nil, fmt.Errorf("parsing template: %v", err)
}
f, err := os.Open(filename)
if err != nil {
return nil, fmt.Errorf("reading file: %v", err)
}
defer f.Close()
records, err := csv.NewReader(f).ReadAll()
if err != nil {
return nil, fmt.Errorf("reading records: %v", err)
}
if len(records) == 0 {
return nil, errors.New("no records to process")
}
var (
b bytes.Buffer
cmds []string
keys = records[0]
vals = make(map[string]string, len(keys))
)
for _, rec := range records[1:] {
for k, v := range rec {
vals[keys[k]] = v
}
if err := t.Execute(&b, vals); err != nil {
return nil, fmt.Errorf("executing template: %v", err)
}
for _, s := range strings.Split(b.String(), ";") {
if cmd := strings.TrimSpace(s); cmd != "" {
cmds = append(cmds, cmd)
}
}
b.Reset()
}
return cmds, nil
}
Edit: Thanks for all the suggestions so far! My question was flagged as being too broad, so I have some specific questions regarding my example.
- Would a test table be useful in a function like this? And, if so, would the test struct need to include the returned
cmds
string slice and the value oferr
? For example:
type tmplTest struct {
name string // test name
tmpl string // the text template
filename string // CSV file with template values
expected []string // expected configuration commands
err error // expected error
}
- How do you handle errors that are supposed to be returned for specific test cases? For example,
os.Open()
returns an error of type*PathError
if an error is encountered. How do I initialize a*PathError
that is equivalent to the one returned byos.Open()
? Same idea fortemplate.Parse()
,template.Execute()
, etc.
Edit 2: Below is a test function I came up with. My two question from the first edit still stand.
package cmd
import (
"testing"
"strings"
"path/filepath"
)
type tmplTest struct {
name string // test name
tmpl string // text template to execute
filename string // CSV containing template text values
cmds []string // expected configuration commands
}
var tests = []tmplTest{
{"empty_error", ``, "", nil},
{"file_error", ``, "fake_file.csv", nil},
{"file_empty_error", ``, "empty.csv", nil},
{"file_fmt_error", ``, "fmt_err.csv", nil},
{"template_fmt_error", `{{ }{{`, "test_values.csv", nil},
{"template_key_error", `{{.InvalidKey}}`, "test_values.csv", nil},
}
func TestGenerateCmds(t *testing.T) {
for _, tc := range tests {
t.Run(tc.name, func(t *testing.T) {
cmds, err := generateCmds(tc.tmpl, filepath.Join("testdata", tc.filename))
if err != nil {
// Unexpected error. Fail the test.
if !strings.Contains(tc.name, "error") {
t.Fatal(err)
}
// TODO: Otherwise, check that the function failed at the expected point.
}
if tc.cmds == nil && cmds != nil {
t.Errorf("expected no commands; got %d", len(cmds))
}
if len(cmds) != len(tc.cmds) {
t.Errorf("expected %d commands; got %d", len(tc.cmds), len(cmds))
}
for i := range cmds {
if cmds[i] != tc.cmds[i] {
t.Errorf("expected %q; got %q", tc.cmds[i], cmds[i])
}
}
})
}
}