Add tests for the sanitizeFilename function

This commit introduces a series of tests for the sanitizeFilename function in msgwriter_test.go. The tests cover various edge cases to ensure filenames are sanitized correctly by replacing or removing invalid characters. These additions will help maintain the integrity and reliability of filename sanitization in the codebase.

msgwriter_test.go

@@ -676,3 +676,33 @@ func TestMsgWriter_writeBody(t *testing.T) {
 		}
 	})
 }
+
+func TestMsgWriter_sanitizeFilename(t *testing.T) {
+	tests := []struct {
+		given string
+		want  string
+	}{
+		{"test.txt", "test.txt"},
+		{"test file.txt", "test file.txt"},
+		{"test\\ file.txt", "test_ file.txt"},
+		{`"test" file.txt`, "_test_ file.txt"},
+		{`test	file	.txt`, "test_file_.txt"},
+		{"test\r\nfile.txt", "test__file.txt"},
+		{"test\x22file.txt", "test_file.txt"},
+		{"test\x2ffile.txt", "test_file.txt"},
+		{"test\x3afile.txt", "test_file.txt"},
+		{"test\x3cfile.txt", "test_file.txt"},
+		{"test\x3efile.txt", "test_file.txt"},
+		{"test\x3ffile.txt", "test_file.txt"},
+		{"test\x5cfile.txt", "test_file.txt"},
+		{"test\x7cfile.txt", "test_file.txt"},
+		{"test\x7ffile.txt", "test_file.txt"},
+	}
+	for _, tt := range tests {
+		t.Run(tt.given+"=>"+tt.want, func(t *testing.T) {
+			if got := sanitizeFilename(tt.given); got != tt.want {
+				t.Errorf("sanitizeFilename failed, expected: %q, got: %q", tt.want, got)
+			}
+		})
+	}
+}