added integration test for good measure

main.go

@@ -237,7 +237,9 @@ func run(c *cli.Context) error {
 			LinkNames: c.Bool("link-names"),
 		},
 	}
-
+	if plugin.Build.Commit == "" {
+		plugin.Build.Commit = "0000000000000000000000000000000000000000"
+	}
 	if plugin.Config.Webhook == "" {
 		return errors.New("Missing webhook")
 	}

plugin.go

@@ -137,14 +137,6 @@ func (p Plugin) Exec() error {
 	return client.PostMessage(&payload)
 }
 
-func detectRef(build Build) string {
-	if build.Commit != "" {
-		return build.Commit[:8]
-	}
-
-	return build.Tag
-}
-
 func templateMessage(t string, plugin Plugin) (string, error) {
 	return template.RenderTrim(t, plugin)
 }
@@ -155,7 +147,7 @@ func message(repo Repo, build Build) string {
 		build.Link,
 		repo.Owner,
 		repo.Name,
-		detectRef(build),
+		build.Commit[:8],
 		build.Branch,
 		build.Author,
 	)
@@ -166,7 +158,7 @@ func fallback(repo Repo, build Build) string {
 		build.Status,
 		repo.Owner,
 		repo.Name,
-		detectRef(build),
+		build.Commit[:8],
 		build.Branch,
 		build.Author,
 	)

plugin_test.go

@@ -1,11 +1,36 @@
 package main
 
 import (
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 
 	"gotest.tools/assert"
 )
 
+func TestExec(t *testing.T) {
+	plugin := Plugin{
+		Repo:   getTestRepo(),
+		Build:  getTestBuild(),
+		Job:    getTestJob(),
+		Config: getTestConfig(),
+	}
+
+	handler := func(w http.ResponseWriter, r *http.Request) {
+		out, _ := ioutil.ReadAll(r.Body)
+		got := string(out)
+		want := `{"attachments":[{"color":"good","fallback":"Message Template Fallback:\nInitial commit\nmaster\nsuccess","text":"Message Template:\nInitial commit\n\nMessage body\nInitial commit\nMessage body","mrkdwn_in":["text","fallback"]}]}`
+		assert.Equal(t, got, want)
+	}
+
+	server := httptest.NewServer(http.HandlerFunc(handler))
+	defer server.Close()
+
+	plugin.Config.Webhook = server.URL
+	plugin.Exec()
+}
+
 func TestNewCommitMessage(t *testing.T) {
 	testCases := map[string]struct {
 		Msg    string
@@ -135,6 +160,12 @@ func getTestBuild() Build {
 	}
 }
 
+func getTestJob() Job {
+	return Job{
+		Started: 1546340400,
+	}
+}
+
 func getTestConfig() Config {
 	t := `Message Template:
 {{build.message}}