Add tests for writeHeader and writeBody functions

Introduce comprehensive test cases for the writeHeader and writeBody functions in msgWriter. These tests cover various scenarios including handling of multiple header values, edge cases, and error conditions in body writing operations. This concludes all tests for msgwriter.go.

msgwriter_test.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"errors"
 	"fmt"
+	"io"
 	"mime"
 	"strings"
 	"testing"
@@ -499,3 +500,115 @@ func TestMsgWriter_writeString(t *testing.T) {
 		}
 	})
 }
+
+func TestMsgWriter_writeHeader(t *testing.T) {
+	msgwriter := &msgWriter{
+		charset: CharsetUTF8,
+		encoder: getEncoder(EncodingQP),
+	}
+	t.Run("writeHeader with single value", func(t *testing.T) {
+		buffer := bytes.NewBuffer(nil)
+		msgwriter.writer = buffer
+		msgwriter.writeHeader(HeaderMessageID, "this.is.a.test")
+		if !strings.EqualFold(buffer.String(), "Message-ID: this.is.a.test\r\n") {
+			t.Errorf("writeHeader failed, expected: %s, got: %s", "Message-ID: this.is.a.test",
+				buffer.String())
+		}
+	})
+	t.Run("writeHeader with multiple values", func(t *testing.T) {
+		buffer := bytes.NewBuffer(nil)
+		msgwriter.writer = buffer
+		msgwriter.writeHeader(HeaderMessageID, "this.is.a.test", "this.as.well")
+		if !strings.EqualFold(buffer.String(), "Message-ID: this.is.a.test, this.as.well\r\n") {
+			t.Errorf("writeHeader failed, expected: %s, got: %s", "Message-ID: this.is.a.test, this.as.well",
+				buffer.String())
+		}
+	})
+	t.Run("writeHeader with no values", func(t *testing.T) {
+		buffer := bytes.NewBuffer(nil)
+		msgwriter.writer = buffer
+		msgwriter.writeHeader(HeaderMessageID)
+		// While technically it is permitted to have empty headers, it's recommend to omit them if
+		// no value is present. We follow this recommendation.
+		if !strings.EqualFold(buffer.String(), "") {
+			t.Errorf("writeHeader failed, expected: %s, got: %s", "", buffer.String())
+		}
+	})
+	t.Run("writeHeader with very long value", func(t *testing.T) {
+		buffer := bytes.NewBuffer(nil)
+		msgwriter.writer = buffer
+		msgwriter.writeHeader(HeaderMessageID, strings.Repeat("a", MaxHeaderLength-13), "next-row")
+		want := "Message-ID:\r\n " + strings.Repeat("a", MaxHeaderLength-13) + ",\r\n next-row\r\n"
+		if !strings.EqualFold(buffer.String(), want) {
+			t.Errorf("writeHeader failed, expected: %s, got: %s", want, buffer.String())
+		}
+	})
+}
+
+func TestMsgWriter_writeBody(t *testing.T) {
+	t.Log("We only cover some edge-cases here, most of the functionality is tested already very thoroughly.")
+
+	msgwriter := &msgWriter{
+		charset: CharsetUTF8,
+		encoder: getEncoder(EncodingQP),
+	}
+	t.Run("writeBody on NoEncoding", func(t *testing.T) {
+		buffer := bytes.NewBuffer(nil)
+		msgwriter.writer = buffer
+		message := testMessage(t)
+		msgwriter.writeBody(message.parts[0].writeFunc, NoEncoding)
+		if msgwriter.err != nil {
+			t.Errorf("writeBody failed to write: %s", msgwriter.err)
+		}
+	})
+	t.Run("writeBody on NoEncoding fails on write", func(t *testing.T) {
+		msgwriter.writer = failReadWriteSeekCloser{}
+		message := testMessage(t)
+		msgwriter.writeBody(message.parts[0].writeFunc, NoEncoding)
+		if msgwriter.err == nil {
+			t.Errorf("writeBody succeeded, expected error")
+		}
+		if !strings.EqualFold(msgwriter.err.Error(), "bodyWriter io.Copy: intentional write failure") {
+			t.Errorf("expected error: bodyWriter io.Copy: intentional write failure, got: %s", msgwriter.err)
+		}
+	})
+	t.Run("writeBody on NoEncoding fails on writeFunc", func(t *testing.T) {
+		buffer := bytes.NewBuffer(nil)
+		msgwriter.writer = buffer
+		writeFunc := func(io.Writer) (int64, error) {
+			return 0, errors.New("intentional write failure")
+		}
+		msgwriter.writeBody(writeFunc, NoEncoding)
+		if msgwriter.err == nil {
+			t.Errorf("writeBody succeeded, expected error")
+		}
+		if !strings.EqualFold(msgwriter.err.Error(), "bodyWriter function: intentional write failure") {
+			t.Errorf("expected error: bodyWriter function: intentional write failure, got: %s", msgwriter.err)
+		}
+	})
+	t.Run("writeBody Quoted-Printable fails on write", func(t *testing.T) {
+		msgwriter.writer = failReadWriteSeekCloser{}
+		message := testMessage(t)
+		msgwriter.writeBody(message.parts[0].writeFunc, EncodingQP)
+		if msgwriter.err == nil {
+			t.Errorf("writeBody succeeded, expected error")
+		}
+		if !strings.EqualFold(msgwriter.err.Error(), "bodyWriter function: intentional write failure") {
+			t.Errorf("expected error: bodyWriter function: intentional write failure, got: %s", msgwriter.err)
+		}
+	})
+	t.Run("writeBody Quoted-Printable fails on writeFunc", func(t *testing.T) {
+		buffer := bytes.NewBuffer(nil)
+		msgwriter.writer = buffer
+		writeFunc := func(io.Writer) (int64, error) {
+			return 0, errors.New("intentional write failure")
+		}
+		msgwriter.writeBody(writeFunc, EncodingQP)
+		if msgwriter.err == nil {
+			t.Errorf("writeBody succeeded, expected error")
+		}
+		if !strings.EqualFold(msgwriter.err.Error(), "bodyWriter function: intentional write failure") {
+			t.Errorf("expected error: bodyWriter function: intentional write failure, got: %s", msgwriter.err)
+		}
+	})
+}