Refactor test cases and remove content print statement

The content print statement in eml.go was removed to optimize code readability and performance. In addition, several assertions in the test cases of eml_test.go were corrected for string formatting errors and a new test case was added for handling emails with attachments. These changes aim to enhance the robustness of tests for email encoding and decoding operations.

eml.go

@@ -365,6 +365,5 @@ func parseEMLAttachmentEmbed(contentDisposition []string, multiPart *multipart.P
 			return fmt.Errorf("failed to embed multipart body: %w", err)
 		}
 	}
-	fmt.Printf("FOUND Content: %s\n", cdType)
 	return nil
 }

eml_test.go

@@ -121,6 +121,37 @@ RGVhciBDdXN0b21lciwKClRoaXMgaXMgYSB0ZXN0IG1haWwuIFBsZWFzZSBkbyBub3QgcmVwbHkg
 dG8gdGhpcy4gQWxzbyB0aGlzIGxpbmUgaXMgdmVyeSBsb25nIHNvIGl0CnNob3VsZCBiZSB3cmFw
 cGVkLgoKClRoYW5rIHlvdXIgZm9yIHlvdXIgYnVzaW5lc3MhClRoZSBnby1tYWlsIHRlYW0KCi0t
 ClRoaXMgaXMgYSBzaWduYXR1cmU=`
+	exampleMailPlainB64WithAttachment = `Date: Wed, 01 Nov 2023 00:00:00 +0000
+MIME-Version: 1.0
+Message-ID: <1305604950.683004066175.AAAAAAAAaaaaaaaaB@go-mail.dev>
+Subject: Example mail // plain text base64 with attachment
+User-Agent: go-mail v0.4.1 // https://github.com/wneessen/go-mail
+X-Mailer: go-mail v0.4.1 // https://github.com/wneessen/go-mail
+From: "Toni Tester" <go-mail@go-mail.dev>
+To: <go-mail+test@go-mail.dev>
+Cc: <go-mail+cc@go-mail.dev>
+Content-Type: multipart/mixed;
+ boundary=45c75ff528359022eb03679fbe91877d75343f2e1f8193e349deffa33ff7
+
+--45c75ff528359022eb03679fbe91877d75343f2e1f8193e349deffa33ff7
+Content-Transfer-Encoding: base64
+Content-Type: text/plain; charset=UTF-8
+
+RGVhciBDdXN0b21lciwKClRoaXMgaXMgYSB0ZXN0IG1haWwuIFBsZWFzZSBkbyBub3QgcmVwbHkg
+dG8gdGhpcy4gQWxzbyB0aGlzIGxpbmUgaXMgdmVyeSBsb25nIHNvIGl0CnNob3VsZCBiZSB3cmFw
+cGVkLgoKClRoYW5rIHlvdXIgZm9yIHlvdXIgYnVzaW5lc3MhClRoZSBnby1tYWlsIHRlYW0KCi0t
+ClRoaXMgaXMgYSBzaWduYXR1cmU=
+
+--45c75ff528359022eb03679fbe91877d75343f2e1f8193e349deffa33ff7
+Content-Disposition: attachment; filename="test.attachment"
+Content-Transfer-Encoding: base64
+Content-Type: application/octet-stream; name="test.attachment"
+
+VGhpcyBpcyBhIHNpbXBsZSB0ZXN0IHRleHQgZmlsZSBhdHRhY2htZW50LgoKSXQgCiAgaGFzCiAg
+ICAgc2V2ZXJhbAogICAgICAgICAgICBuZXdsaW5lcwoJICAgICAgICAgICAgYW5kCgkgICAgc3Bh
+Y2VzCiAgICAgaW4KICBpdAouCgpBcyB3ZWxsIGFzIGFuIGVtb2ppOiDwn5mCCg==
+
+--45c75ff528359022eb03679fbe91877d75343f2e1f8193e349deffa33ff7--`
 )
 
 func TestEMLToMsgFromString(t *testing.T) {
@@ -147,13 +178,13 @@ func TestEMLToMsgFromString(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			msg, err := EMLToMsgFromString(tt.eml)
 			if err != nil {
-				t.Errorf("failed to parse EML: %subject", err)
+				t.Errorf("failed to parse EML: %s", err)
 			}
 			if msg.Encoding() != tt.enc {
-				t.Errorf("EMLToMsgFromString failed: expected encoding: %subject, but got: %subject", tt.enc, msg.Encoding())
+				t.Errorf("EMLToMsgFromString failed: expected encoding: %s, but got: %s", tt.enc, msg.Encoding())
 			}
 			if subject := msg.GetGenHeader(HeaderSubject); len(subject) > 0 && !strings.EqualFold(subject[0], tt.sub) {
-				t.Errorf("EMLToMsgFromString failed: expected subject: %subject, but got: %subject",
+				t.Errorf("EMLToMsgFromString failed: expected subject: %s, but got: %s",
 					tt.sub, subject[0])
 			}
 		})
@@ -199,13 +230,13 @@ func TestEMLToMsgFromFile(t *testing.T) {
 			}
 			msg, err := EMLToMsgFromFile(fmt.Sprintf("%s/%s.eml", tempDir, tt.name))
 			if err != nil {
-				t.Errorf("failed to parse EML: %subject", err)
+				t.Errorf("failed to parse EML: %s", err)
 			}
 			if msg.Encoding() != tt.enc {
-				t.Errorf("EMLToMsgFromString failed: expected encoding: %subject, but got: %subject", tt.enc, msg.Encoding())
+				t.Errorf("EMLToMsgFromString failed: expected encoding: %s, but got: %s", tt.enc, msg.Encoding())
 			}
 			if subject := msg.GetGenHeader(HeaderSubject); len(subject) > 0 && !strings.EqualFold(subject[0], tt.sub) {
-				t.Errorf("EMLToMsgFromString failed: expected subject: %subject, but got: %subject",
+				t.Errorf("EMLToMsgFromString failed: expected subject: %s, but got: %s",
 					tt.sub, subject[0])
 			}
 		})
@@ -232,3 +263,33 @@ func TestEMLToMsgFromStringBrokenDate(t *testing.T) {
 		t.Errorf("EML with no date expected: %s, got: %s", now.Format(time.RFC1123Z), d)
 	}
 }
+
+func TestEMLToMsgFromStringWithAttachment(t *testing.T) {
+	wantSubject := "Example mail // plain text base64 with attachment"
+	msg, err := EMLToMsgFromString(exampleMailPlainB64WithAttachment)
+	if err != nil {
+		t.Errorf("EML with attachment failed: %s", err)
+	}
+	if subject := msg.GetGenHeader(HeaderSubject); len(subject) > 0 && !strings.EqualFold(subject[0], wantSubject) {
+		t.Errorf("EMLToMsgFromString of EML with attachment failed: expected subject: %s, but got: %s",
+			wantSubject, subject[0])
+	}
+	if len(msg.attachments) != 1 {
+		t.Errorf("EMLToMsgFromString of EML with attachment failed: expected no. of attachments: %d, but got: %d",
+			1, len(msg.attachments))
+	}
+	contentTypeHeader := msg.GetGenHeader(HeaderContentType)
+	if len(contentTypeHeader) != 1 {
+		t.Errorf("EMLToMsgFromString of EML with attachment failed: expected no. of content-type header: %d, "+
+			"but got: %d", 1, len(contentTypeHeader))
+	}
+	contentTypeSplit := strings.SplitN(contentTypeHeader[0], "; ", 2)
+	if len(contentTypeSplit) != 2 {
+		t.Error("failed to split Content-Type header")
+		return
+	}
+	if !strings.EqualFold(contentTypeSplit[0], "multipart/mixed") {
+		t.Errorf("EMLToMsgFromString of EML with attachment failed: expected content-type: %s, "+
+			"but got: %s", "multipart/mixed", contentTypeSplit[0])
+	}
+}