test(lint): task lint must exit non-zero on a finding (#41), red

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

test/lintgate/lintgate_test.go

@@ -0,0 +1,97 @@
+package lintgate
+
+// Observes the exit status of `task lint` (the lint step of `task check`), not the lint
+// rules themselves. It runs the repo's real Taskfile in a scratch module so a change to the
+// lint command that stops it failing on findings (#41) turns this red.
+
+import (
+	"bytes"
+	"errors"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+const scratchWithFinding = `package main
+
+import "os"
+
+func main() { os.Remove("x") }
+`
+
+func scratchModule(t *testing.T) string {
+	t.Helper()
+	taskfile, err := os.ReadFile(filepath.Join("..", "..", "Taskfile.yml"))
+	if err != nil {
+		t.Fatalf("read Taskfile.yml: %v", err)
+	}
+	dir := t.TempDir()
+	for name, body := range map[string]string{
+		"Taskfile.yml": string(taskfile),
+		"go.mod":       "module scratch\n\ngo 1.21\n",
+		"main.go":      scratchWithFinding,
+	} {
+		if err := os.WriteFile(filepath.Join(dir, name), []byte(body), 0o644); err != nil {
+			t.Fatalf("write %s: %v", name, err)
+		}
+	}
+	return dir
+}
+
+// runLint runs `task lint` in dir with the given PATH and returns its combined output and exit code.
+func runLint(t *testing.T, dir, path string) (string, int) {
+	t.Helper()
+	taskBin, err := exec.LookPath("task")
+	if err != nil {
+		t.Skip("task not installed")
+	}
+	cmd := exec.Command(taskBin, "lint")
+	cmd.Dir = dir
+	cmd.Env = append(os.Environ(), "PATH="+path)
+	var out bytes.Buffer
+	cmd.Stdout, cmd.Stderr = &out, &out
+	err = cmd.Run()
+	var exitErr *exec.ExitError
+	switch {
+	case err == nil:
+		return out.String(), 0
+	case errors.As(err, &exitErr):
+		return out.String(), exitErr.ExitCode()
+	default:
+		t.Fatalf("run task lint: %v", err)
+		return "", -1
+	}
+}
+
+func TestTaskLint_ExitsNonZeroWhenGolangciLintReportsAFinding(t *testing.T) {
+	if _, err := exec.LookPath("golangci-lint"); err != nil {
+		t.Skip("golangci-lint not installed")
+	}
+	out, code := runLint(t, scratchModule(t), os.Getenv("PATH"))
+	if code == 0 {
+		t.Fatalf("task lint exited 0 on a module with an unchecked error; output:\n%s", out)
+	}
+	if strings.Contains(out, "not installed") {
+		t.Fatalf("task lint blamed a missing binary for a lint failure; output:\n%s", out)
+	}
+}
+
+func TestTaskLint_SkipsWithANoticeWhenGolangciLintIsAbsent(t *testing.T) {
+	taskBin, err := exec.LookPath("task")
+	if err != nil {
+		t.Skip("task not installed")
+	}
+	bin := t.TempDir() // a PATH holding task and nothing else
+	if err := os.Symlink(taskBin, filepath.Join(bin, "task")); err != nil {
+		t.Fatalf("symlink task: %v", err)
+	}
+	out, code := runLint(t, scratchModule(t), bin)
+	if code != 0 {
+		t.Fatalf("task lint exited %d without golangci-lint on PATH; output:\n%s", code, out)
+	}
+	if !strings.Contains(out, "not installed") {
+		t.Fatalf("expected the skip notice; output:\n%s", out)
+	}
+}