Printer: add tests (#126)

* printer: add tests

* printer: add license to test file

* Update printer/printer_test.go

Co-Authored-By: Miguel de la Cruz <mgdelacroix@gmail.com>

* Update printer/printer_test.go

Co-Authored-By: Miguel de la Cruz <mgdelacroix@gmail.com>

* printer: incorporate review comments

* printer: add tests for check to if json output clears buffer

Co-authored-by: mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Miguel de la Cruz <mgdelacroix@gmail.com>

printer/printer.go

@@ -7,6 +7,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"fmt"
+	"io"
 	"os"
 	"text/template"
 )
@@ -17,6 +18,9 @@ const (
 )
 
 type Printer struct {
+	writer  io.Writer
+	eWriter io.Writer
+
 	Format     string
 	Single     bool
 	Lines      []interface{}
@@ -25,20 +29,25 @@ type Printer struct {
 
 var printer Printer
 
-// Sets the format for the final output of the printer
+func init() {
+	printer.writer = os.Stdout
+	printer.eWriter = os.Stderr
+}
+
+// SetFormat sets the format for the final output of the printer
 func SetFormat(t string) {
 	printer.Format = t
 }
 
-// Sets the single flag on the printer. If this flag is set, the
+// SetSingle sets the single flag on the printer. If this flag is set, the
 // printer will check the size of stored elements before printing, and
 // if there is only one, it will be printed on its own instead of
 // inside a list
 func SetSingle(single bool) {
 	printer.Single = single
 }
 
-// Prints an element. Depending on the format, the element can be
+// PrintT prints an element. Depending on the format, the element can be
 // formatted and printed as a structure or used to populate the
 // template
 func PrintT(templateString string, v interface{}) {
@@ -51,20 +60,20 @@ func PrintT(templateString string, v interface{}) {
 		}
 		tplString := tpl.String()
 		printer.Lines = append(printer.Lines, tplString)
-		fmt.Println(tplString)
+		fmt.Fprintln(printer.writer, tplString)
 	case FormatJSON:
 		printer.Lines = append(printer.Lines, v)
 	}
 }
 
-// Prints an element. If the format requires a template, the element
+// Print an element. If the format requires a template, the element
 // will be printed as a structure with field names using the print
 // verb %+v
 func Print(v interface{}) {
 	PrintT("{{printf \"%+v\" .}}", v)
 }
 
-// Prints the elements accumulated in the printer
+// Flush writes the elements accumulated in the printer
 func Flush() {
 	if printer.Format == FormatJSON {
 		var b []byte
@@ -74,29 +83,29 @@ func Flush() {
 			b, _ = json.MarshalIndent(printer.Lines, "", "  ")
 		}
 
-		fmt.Println(string(b))
+		fmt.Fprintln(printer.writer, string(b))
 		printer.Lines = []interface{}{}
 	}
 }
 
-// Resets the printer's accumulated lines
+// Clean resets the printer's accumulated lines
 func Clean() {
 	printer.Lines = []interface{}{}
 	printer.ErrorLines = []interface{}{}
 }
 
-// Returns the printer's accumulated lines
+// GetLines returns the printer's accumulated lines
 func GetLines() []interface{} {
 	return printer.Lines
 }
 
-// Returns the printer's accumulated error lines
+// GetErrorLines returns the printer's accumulated error lines
 func GetErrorLines() []interface{} {
 	return printer.ErrorLines
 }
 
-// Prints an error string to the stderr.
+// PrintError prints to the stderr.
 func PrintError(msg string) {
 	printer.ErrorLines = append(printer.ErrorLines, msg)
-	fmt.Fprintln(os.Stderr, msg)
+	fmt.Fprintln(printer.eWriter, msg)
 }

printer/printer_test.go

@@ -0,0 +1,81 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package printer
+
+import (
+	"bufio"
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type mockWriter []byte
+
+func (w *mockWriter) Write(b []byte) (n int, err error) {
+	*w = append(*w, b...)
+	return len(*w) - len(b), nil
+}
+
+func TestPrintT(t *testing.T) {
+	w := bufio.NewWriter(&bytes.Buffer{})
+	printer.writer = w
+	printer.Format = FormatPlain
+
+	ts := struct {
+		ID int
+	}{
+		ID: 123,
+	}
+
+	t.Run("should execute template", func(t *testing.T) {
+		tpl := `testing template {{.ID}}`
+		PrintT(tpl, ts)
+		assert.Len(t, GetLines(), 1)
+
+		Flush()
+		assert.Equal(t, "testing template 123", printer.Lines[0])
+	})
+
+	t.Run("should fail to execute, no method or field", func(t *testing.T) {
+		Clean()
+		tpl := `testing template {{.Name}}`
+		PrintT(tpl, ts)
+		assert.Len(t, GetErrorLines(), 1)
+
+		Flush()
+		assert.Equal(t, "Can't print the message using the provided template: "+tpl, printer.ErrorLines[0])
+	})
+}
+
+func TestFlush(t *testing.T) {
+	printer.Format = FormatJSON
+
+	t.Run("should print a line in JSON format", func(t *testing.T) {
+		mw := &mockWriter{}
+		printer.writer = mw
+		Clean()
+
+		Print("test string")
+		assert.Len(t, GetLines(), 1)
+
+		Flush()
+		assert.Equal(t, "[\n  \"test string\"\n]\n", string(*mw))
+		assert.Empty(t, GetLines(), 0)
+	})
+
+	t.Run("should print multi line in JSON format", func(t *testing.T) {
+		mw := &mockWriter{}
+		printer.writer = mw
+
+		Clean()
+		Print("test string-1")
+		Print("test string-2")
+		assert.Len(t, GetLines(), 2)
+
+		Flush()
+		assert.Equal(t, "[\n  \"test string-1\",\n  \"test string-2\"\n]\n", string(*mw))
+		assert.Empty(t, GetLines(), 0)
+	})
+}