diff --git a/src/cfdp/pdu/metadata.rs b/src/cfdp/pdu/metadata.rs
index 90303d3..646d03b 100644
--- a/src/cfdp/pdu/metadata.rs
+++ b/src/cfdp/pdu/metadata.rs
@@ -340,7 +340,10 @@ impl CfdpPdu for MetadataPduReader<'_> {
 
 #[cfg(test)]
 pub mod tests {
+    use alloc::string::ToString;
+
     use crate::cfdp::lv::Lv;
+    use crate::cfdp::pdu::eof::EofPdu;
     use crate::cfdp::pdu::metadata::{
         build_metadata_opts_from_slice, build_metadata_opts_from_vec, MetadataGenericParams,
         MetadataPduCreator, MetadataPduReader,
@@ -348,7 +351,7 @@ pub mod tests {
     use crate::cfdp::pdu::tests::{
         common_pdu_conf, verify_raw_header, TEST_DEST_ID, TEST_SEQ_NUM, TEST_SRC_ID,
     };
-    use crate::cfdp::pdu::{CfdpPdu, WritablePduPacket};
+    use crate::cfdp::pdu::{CfdpPdu, PduError, WritablePduPacket};
     use crate::cfdp::pdu::{FileDirectiveType, PduHeader};
     use crate::cfdp::tlv::{Tlv, TlvType};
     use crate::cfdp::{
@@ -600,6 +603,45 @@ pub mod tests {
         assert_eq!(accumulated_len, pdu_read_back.options().len());
     }
 
+    #[test]
+    fn test_invalid_directive_code() {
+        let (_, _, metadata_pdu) = generic_metadata_pdu(CrcFlag::NoCrc, LargeFileFlag::Large, &[]);
+        let mut metadata_vec = metadata_pdu.to_vec().unwrap();
+        metadata_vec[7] = 0xff;
+        let metadata_error = MetadataPduReader::from_bytes(&metadata_vec);
+        assert!(metadata_error.is_err());
+        let error = metadata_error.unwrap_err();
+        if let PduError::InvalidDirectiveType { found, expected } = error {
+            assert_eq!(found, 0xff);
+            assert_eq!(expected, Some(FileDirectiveType::MetadataPdu));
+            assert_eq!(
+                error.to_string(),
+                "invalid directive type value 255, expected Some(MetadataPdu)"
+            );
+        } else {
+            panic!("Expected InvalidDirectiveType error, got {:?}", error);
+        }
+    }
+
+    #[test]
+    fn test_wrong_directive_code() {
+        let (_, _, metadata_pdu) = generic_metadata_pdu(CrcFlag::NoCrc, LargeFileFlag::Large, &[]);
+        let mut metadata_vec = metadata_pdu.to_vec().unwrap();
+        metadata_vec[7] = FileDirectiveType::EofPdu as u8;
+        let metadata_error = MetadataPduReader::from_bytes(&metadata_vec);
+        assert!(metadata_error.is_err());
+        let error = metadata_error.unwrap_err();
+        if let PduError::WrongDirectiveType { found, expected } = error {
+            assert_eq!(found, FileDirectiveType::EofPdu);
+            assert_eq!(expected, FileDirectiveType::MetadataPdu);
+            assert_eq!(
+                error.to_string(),
+                "found directive type EofPdu, expected MetadataPdu"
+            );
+        } else {
+            panic!("Expected InvalidDirectiveType error, got {:?}", error);
+        }
+    }
     #[test]
     fn test_corrects_pdu_header() {
         let pdu_header = PduHeader::new_for_file_data(
diff --git a/src/cfdp/pdu/mod.rs b/src/cfdp/pdu/mod.rs
index 5520536..2fb8516 100644
--- a/src/cfdp/pdu/mod.rs
+++ b/src/cfdp/pdu/mod.rs
@@ -55,7 +55,6 @@ pub enum PduError {
         found: u8,
         expected: Option<FileDirectiveType>,
     },
-    InvalidSegmentRequestFormat,
     InvalidStartOrEndOfScopeValue,
     /// Invalid condition code. Contains the raw detected value.
     InvalidConditionCode(u8),
@@ -80,9 +79,6 @@ impl Display for PduError {
                     "invalid PDU entity ID length {raw_id}, only [1, 2, 4, 8] are allowed"
                 )
             }
-            PduError::InvalidSegmentRequestFormat => {
-                write!(f, "invalid segment request format for NAK PDU")
-            }
             PduError::InvalidStartOrEndOfScopeValue => {
                 write!(f, "invalid start or end of scope for NAK PDU")
             }
@@ -855,6 +851,7 @@ mod tests {
         // 4 byte fixed header plus three bytes src, dest ID and transaction ID
         assert_eq!(res.unwrap(), 7);
         verify_raw_header(&pdu_header, &buf);
+        assert_eq!(pdu_header.pdu_datafield_len(), 5);
     }
 
     #[test]
@@ -948,7 +945,10 @@ mod tests {
         let error = res.unwrap_err();
         if let PduError::CfdpVersionMissmatch(raw_version) = error {
             assert_eq!(raw_version, CFDP_VERSION_2 + 1);
-            assert_eq!(error.to_string(), "cfdp version missmatch, found 2, expected 1");
+            assert_eq!(
+                error.to_string(),
+                "cfdp version missmatch, found 2, expected 1"
+            );
         } else {
             panic!("invalid exception: {}", error);
         }
@@ -1048,6 +1048,10 @@ mod tests {
         {
             assert_eq!(src_id_len, 1);
             assert_eq!(dest_id_len, 2);
+            assert_eq!(
+                error.to_string(),
+                "missmatch of PDU source length 1 and destination length 2"
+            );
         }
     }
 
@@ -1110,7 +1114,7 @@ mod tests {
     fn test_pdu_config_clonable_and_comparable() {
         let common_pdu_cfg_0 =
             CommonPduConfig::new_with_byte_fields(UbfU8::new(1), UbfU8::new(2), UbfU8::new(3))
-            .expect("common config creation failed");
+                .expect("common config creation failed");
         let common_pdu_cfg_1 = common_pdu_cfg_0;
         assert_eq!(common_pdu_cfg_0, common_pdu_cfg_1);
     }
diff --git a/src/cfdp/pdu/nak.rs b/src/cfdp/pdu/nak.rs
index 3b34903..3a7a38a 100644
--- a/src/cfdp/pdu/nak.rs
+++ b/src/cfdp/pdu/nak.rs
@@ -501,6 +501,8 @@ impl<'a, 'b> PartialEq<NakPduCreator<'a>> for NakPduReader<'b> {
 
 #[cfg(test)]
 mod tests {
+    use alloc::string::ToString;
+
     use crate::cfdp::{
         pdu::tests::{common_pdu_conf, verify_raw_header, TEST_DEST_ID, TEST_SEQ_NUM, TEST_SRC_ID},
         PduType, TransmissionMode,
@@ -742,11 +744,14 @@ mod tests {
             Some(u32_list),
         );
         assert!(error.is_err());
-
-        if let Err(PduError::InvalidStartOrEndOfScopeValue) = error {
-            assert_eq!(error.to_string(), )
+        let error = error.unwrap_err();
+        if let PduError::InvalidStartOrEndOfScopeValue = error {
+            assert_eq!(
+                error.to_string(),
+                "invalid start or end of scope for NAK PDU"
+            );
         } else {
-            panic!("API call did not fail");
+            panic!("unexpected error {error}");
         }
     }