diff --git a/stream/mts/psi/descriptor_test.go b/stream/mts/psi/descriptor_test.go
new file mode 100644
index 00000000..cb25761c
--- /dev/null
+++ b/stream/mts/psi/descriptor_test.go
@@ -0,0 +1,224 @@
+/*
+NAME
+  descriptor_test.go
+
+DESCRIPTION
+  See Readme.md
+
+AUTHOR
+  Saxon Nelson-Milton <saxon@ausocean.org>
+
+LICENSE
+  descriptor_test.go is Copyright (C) 2017-2019 the Australian Ocean Lab (AusOcean)
+
+  It is free software: you can redistribute it and/or modify them
+  under the terms of the GNU General Public License as published by the
+  Free Software Foundation, either version 3 of the License, or (at your
+  option) any later version.
+
+  It is distributed in the hope that it will be useful, but WITHOUT
+  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with revid in gpl.txt.  If not, see http://www.gnu.org/licenses.
+*/
+
+package psi
+
+import (
+	"bytes"
+	"testing"
+)
+
+const (
+	errNotExpectedOut = "Did not get expected output: \ngot : %v, \nwant: %v"
+)
+
+var tstPsi1 = PSI{
+	Pf:  0x00,
+	Tid: 0x02,
+	Ssi: true,
+	Sl:  0x1c,
+	Tss: &TSS{
+		Tide: 0x01,
+		V:    0,
+		Cni:  true,
+		Sn:   0,
+		Lsn:  0,
+		Sd: &PMT{
+			Pcrpid: 0x0100, // wrong
+			Pil:    10,
+			Pd: []Desc{
+				{
+					Dt: TimeDescTag,
+					Dl: TimeDataSize,
+					Dd: make([]byte, TimeDataSize),
+				},
+			},
+			Essd: &ESSD{
+				St:   0x1b,
+				Epid: 0x0100,
+				Esil: 0x00,
+			},
+		},
+	},
+}
+
+var tstPsi2 = PSI{
+	Pf:  0x00,
+	Tid: 0x02,
+	Ssi: true,
+	Sl:  0x12,
+	Tss: &TSS{
+		Tide: 0x01,
+		V:    0,
+		Cni:  true,
+		Sn:   0,
+		Lsn:  0,
+		Sd: &PMT{
+			Pcrpid: 0x0100,
+			Pil:    0,
+			Essd: &ESSD{
+				St:   0x1b,
+				Epid: 0x0100,
+				Esil: 0x00,
+			},
+		},
+	},
+}
+
+var tstPsi3 = PSI{
+	Pf:  0x00,
+	Tid: 0x02,
+	Ssi: true,
+	Sl:  0x3e,
+	Tss: &TSS{
+		Tide: 0x01,
+		V:    0,
+		Cni:  true,
+		Sn:   0,
+		Lsn:  0,
+		Sd: &PMT{
+			Pcrpid: 0x0100,
+			Pil:    PmtTimeLocationPil,
+			Pd: []Desc{
+				{
+					Dt: TimeDescTag,
+					Dl: TimeDataSize,
+					Dd: make([]byte, TimeDataSize),
+				},
+				{
+					Dt: LocationDescTag,
+					Dl: LocationDataSize,
+					Dd: make([]byte, LocationDataSize),
+				},
+			},
+			Essd: &ESSD{
+				St:   0x1b,
+				Epid: 0x0100,
+				Esil: 0x00,
+			},
+		},
+	},
+}
+
+func TestHasDescriptor(t *testing.T) {
+	p := PSIBytes(tstPsi3.Bytes())
+
+	// Try getting descriptor that exists
+	got := p.HasDescriptor(LocationDescTag)
+	want := []byte{
+		LocationDescTag,
+		LocationDataSize,
+	}
+	want = append(want, make([]byte, LocationDataSize)...)
+
+	if !bytes.Equal(got, want) {
+		t.Errorf(errNotExpectedOut, got, want)
+	}
+
+	// Try getting descriptor that doesnt exist
+	const fakeTag = 236
+	got = p.HasDescriptor(fakeTag)
+	want = nil
+
+	if !bytes.Equal(got, want) {
+		t.Errorf(errNotExpectedOut, got, want)
+	}
+
+	// Try getting descriptor from psi that has no descriptors
+	p = PSIBytes(tstPsi2.Bytes())
+
+	got = p.HasDescriptor(LocationDescTag)
+	want = nil
+
+	if !bytes.Equal(got, want) {
+		t.Errorf(errNotExpectedOut, got, want)
+	}
+}
+
+func TestProgramInfoLen(t *testing.T) {
+	p := PSIBytes(tstPsi1.Bytes())
+	got := p.ProgramInfoLen()
+	want := 10
+	if got != want {
+		t.Errorf(errNotExpectedOut, got, want)
+	}
+}
+
+func TestDescriptors(t *testing.T) {
+	// Try psi with descriptors
+	p := PSIBytes(tstPsi1.Bytes())
+	got := p.descriptors()
+	want := []byte{
+		TimeDescTag,
+		TimeDataSize,
+	}
+	want = append(want, make([]byte, TimeDataSize)...)
+
+	if !bytes.Equal(got, want) {
+		t.Errorf(errNotExpectedOut, got, want)
+	}
+
+	// Now try psi with empty descriptors
+	p = PSIBytes(tstPsi2.Bytes())
+	got = p.descriptors()
+	want = nil
+	if !bytes.Equal(got, want) {
+		t.Errorf(errNotExpectedOut, got, want)
+	}
+}
+
+func TestCreateDescriptor(t *testing.T) {
+	// Test with PSI containing no descriptors
+	p := PSIBytes(tstPsi2.Bytes())
+	p.createDescriptor(TimeDescTag, make([]byte, TimeDataSize))
+	// update crc
+	noPadding := p.trimPadding()
+	updateCrc(noPadding[1:])
+	want := PSIBytes(tstPsi1.Bytes())
+	got := p
+
+	if !bytes.Equal(want, got) {
+		t.Errorf(errNotExpectedOut, got, want)
+	}
+
+	// Test with psi containing descriptor already
+	p = PSIBytes(tstPsi1.Bytes())
+	p.createDescriptor(LocationDescTag, make([]byte, LocationDataSize))
+	// update crc
+	noPadding = p.trimPadding()
+	updateCrc(noPadding[1:])
+	want = PSIBytes(tstPsi3.Bytes())
+	got = p
+
+	if !bytes.Equal(want, got) {
+		t.Errorf(errNotExpectedOut, got, want)
+	}
+}
+
+func TestUpdateDescriptor(t *testing.T) {
+
+}