diff --git a/src/uslp/mod.rs b/src/uslp/mod.rs
index 2e8b803..d6f6555 100644
--- a/src/uslp/mod.rs
+++ b/src/uslp/mod.rs
@@ -596,6 +596,31 @@ mod tests {
         assert_eq!(primary_header.vc_frame_count(), 5);
     }
 
+    #[test]
+    fn test_vcf_count_len_one() {
+        let mut buf: [u8; 16] = [0; 16];
+        // Should be all zeros after writing.
+        buf[6] = 0xff;
+        let mut primary_header = PrimaryHeader::new(
+            0b10100101_11000011,
+            SourceOrDestField::Dest,
+            0b110101,
+            0b1010,
+            0x2345,
+        )
+        .unwrap();
+        primary_header.set_vc_frame_count(1, 255).unwrap();
+        assert_eq!(primary_header.vc_frame_count_len(), 1);
+        assert_eq!(primary_header.vc_frame_count(), 255);
+        assert_eq!(primary_header.write_to_be_bytes(&mut buf).unwrap(), 8);
+        assert_eq!(buf[6] & 0b111, 1);
+        assert_eq!(buf[7], 255);
+
+        let primary_header = PrimaryHeader::from_bytes(&buf).unwrap();
+        assert_eq!(primary_header.vc_frame_count_len(), 1);
+        assert_eq!(primary_header.vc_frame_count(), 255);
+    }
+
     #[test]
     fn test_reading_0() {
         let mut buf: [u8; 8] = [0; 8];
@@ -840,4 +865,77 @@ mod tests {
             UslpError::InvalidVersionNumber(0)
         );
     }
+
+    #[test]
+    fn test_primary_header_buf_too_small() {
+        let primary_header = PrimaryHeader::new(
+            0b10100101_11000011,
+            SourceOrDestField::Dest,
+            0b110101,
+            0b1010,
+            0x2345,
+        )
+        .unwrap();
+        if let Err(ByteConversionError::ToSliceTooSmall { found, expected }) =
+            primary_header.write_to_be_bytes(&mut [0; 4])
+        {
+            assert_eq!(found, 4);
+            assert_eq!(expected, 7);
+        } else {
+            panic!("writing primary header did not fail or failed with wrong error");
+        }
+    }
+
+    #[test]
+    fn test_applicability_contr_rules() {
+        assert!(ConstructionRule::PacketSpanningMultipleFrames.applicable_to_fixed_len_tfdz());
+        assert!(ConstructionRule::StartOfMapaSduOrVcaSdu.applicable_to_fixed_len_tfdz());
+        assert!(ConstructionRule::ContinuingPortionOfMapaSdu.applicable_to_fixed_len_tfdz());
+        assert!(!ConstructionRule::OctetStream.applicable_to_fixed_len_tfdz());
+        assert!(!ConstructionRule::StartingSegment.applicable_to_fixed_len_tfdz());
+        assert!(!ConstructionRule::ContinuingSegment.applicable_to_fixed_len_tfdz());
+        assert!(!ConstructionRule::LastSegment.applicable_to_fixed_len_tfdz());
+        assert!(!ConstructionRule::NoSegmentation.applicable_to_fixed_len_tfdz());
+    }
+
+    #[test]
+    fn test_header_len_correctness() {
+        let mut tfdh = TransferFrameDataFieldHeader {
+            construction_rule: ConstructionRule::PacketSpanningMultipleFrames,
+            uslp_protocol_id: UslpProtocolId::UserDefinedOctetStream,
+            fhp_or_lvo: Some(0),
+        };
+        assert_eq!(tfdh.len_header(), 3);
+        tfdh = TransferFrameDataFieldHeader {
+            construction_rule: ConstructionRule::StartOfMapaSduOrVcaSdu,
+            uslp_protocol_id: UslpProtocolId::UserDefinedOctetStream,
+            fhp_or_lvo: Some(0),
+        };
+        assert_eq!(tfdh.len_header(), 3);
+        tfdh = TransferFrameDataFieldHeader {
+            construction_rule: ConstructionRule::ContinuingPortionOfMapaSdu,
+            uslp_protocol_id: UslpProtocolId::UserDefinedOctetStream,
+            fhp_or_lvo: Some(0),
+        };
+        assert_eq!(tfdh.len_header(), 3);
+        tfdh = TransferFrameDataFieldHeader {
+            construction_rule: ConstructionRule::OctetStream,
+            uslp_protocol_id: UslpProtocolId::UserDefinedOctetStream,
+            fhp_or_lvo: None,
+        };
+        assert_eq!(tfdh.len_header(), 1);
+    }
+
+    #[test]
+    fn test_frame_data_field_header_from_bytes_too_small() {
+        let buf: [u8; 0] = [];
+        assert_eq!(
+            TransferFrameDataFieldHeader::from_bytes(&buf).unwrap_err(),
+            ByteConversionError::FromSliceTooSmall {
+                found: 0,
+                expected: 1
+            }
+            .into()
+        );
+    }
 }