Add JSON test.

cmd/decouple/decouple_test.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"path/filepath"
+	"reflect"
+	"testing"
+)
+
+func TestRun(t *testing.T) {
+	buf := new(bytes.Buffer)
+	if err := run(buf, false, true, []string{"../.."}); err != nil {
+		t.Fatal(err)
+	}
+
+	var (
+		got []jtuple
+		dec = json.NewDecoder(buf)
+	)
+	for dec.More() {
+		var val jtuple
+		if err := dec.Decode(&val); err != nil {
+			t.Fatal(err)
+		}
+		val.FileName = filepath.Base(val.FileName)
+		got = append(got, val)
+	}
+
+	want := []jtuple{{
+		PackageName: "main",
+		FileName:    "main.go",
+		Line:        100,
+		FuncName:    "showJSON",
+		Params: []jparam{{
+			Name: "checker",
+			Methods: []string{
+				"NameForMethods",
+			},
+		}},
+	}}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Errorf("got %v, want %v", got, want)
+	}
+}

cmd/decouple/main.go

@@ -4,9 +4,11 @@ import (
 	"encoding/json"
 	"flag"
 	"fmt"
+	"io"
 	"os"
 	"sort"
 
+	"github.com/bobg/errors"
 	"github.com/bobg/go-generics/v3/maps"
 
 	"github.com/bobg/decouple"
@@ -21,28 +23,32 @@ func main() {
 	flag.BoolVar(&doJSON, "json", false, "output in JSON format")
 	flag.Parse()
 
+	if err := run(os.Stdout, verbose, doJSON, flag.Args()); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(1)
+	}
+}
+
+func run(w io.Writer, verbose, doJSON bool, args []string) error {
 	var dir string
-	switch flag.NArg() {
+	switch len(args) {
 	case 0:
 		dir = "."
 	case 1:
-		dir = flag.Arg(0)
+		dir = args[0]
 	default:
-		fmt.Fprintf(os.Stderr, "Usage: %s [-v] [DIR]\n", os.Args[0])
-		os.Exit(1)
+		return fmt.Errorf("Usage: %s [-v] [-json] [DIR]", os.Args[0])
 	}
 
 	checker, err := decouple.NewCheckerFromDir(dir)
 	if err != nil {
-		fmt.Fprintln(os.Stderr, err)
-		os.Exit(1)
+		return errors.Wrapf(err, "creating checker for %s", dir)
 	}
 	checker.Verbose = verbose
 
 	tuples, err := checker.Check()
 	if err != nil {
-		fmt.Fprintln(os.Stderr, err)
-		os.Exit(1)
+		return errors.Wrapf(err, "checking %s", dir)
 	}
 
 	sort.Slice(tuples, func(i, j int) bool {
@@ -57,11 +63,8 @@ func main() {
 	})
 
 	if doJSON {
-		if err := showJSON(checker, tuples); err != nil {
-			fmt.Fprintln(os.Stderr, err)
-			os.Exit(1)
-		}
-		return
+		err := showJSON(w, checker, tuples)
+		return errors.Wrap(err, "formatting JSON output")
 	}
 
 	for _, tuple := range tuples {
@@ -76,24 +79,26 @@ func main() {
 			}
 
 			if !showedFuncName {
-				fmt.Printf("%s: %s\n", tuple.Pos(), tuple.F.Name.Name)
+				fmt.Fprintf(w, "%s: %s\n", tuple.Pos(), tuple.F.Name.Name)
 				showedFuncName = true
 			}
 
 			if intfName := checker.NameForMethods(mm); intfName != "" {
-				fmt.Printf("    %s: %s\n", param, intfName)
+				fmt.Fprintf(w, "    %s: %s\n", param, intfName)
 				continue
 			}
 
 			methods := maps.Keys(tuple.M[param])
 			sort.Strings(methods)
-			fmt.Printf("    %s: %v\n", param, methods)
+			fmt.Fprintf(w, "    %s: %v\n", param, methods)
 		}
 	}
+
+	return nil
 }
 
-func showJSON(checker decouple.Checker, tuples []decouple.Tuple) error {
-	enc := json.NewEncoder(os.Stdout)
+func showJSON(w io.Writer, checker decouple.Checker, tuples []decouple.Tuple) error {
+	enc := json.NewEncoder(w)
 	enc.SetIndent("", "  ")
 
 	for _, tuple := range tuples {