Fix unit test, it should return after any error is returned from Decode

function whether expected or not, rather than continue and try to
compare invalid decoded results.

Extend the unit test slightly to check the header.

Remove go-test/deep dependency in favour of standard library reflect
package.

function_call_test.go

@@ -1,7 +1,8 @@
 package pgproto3
 
 import (
-	"github.com/go-test/deep"
+	"encoding/binary"
+	"reflect"
 	"testing"
 )
 
@@ -17,7 +18,7 @@ func TestFunctionCall_EncodeDecode(t *testing.T) {
 		fields  fields
 		wantErr bool
 	}{
-		{"foo", fields{uint32(123), []uint16{0, 1, 0, 1}, [][]byte{[]byte("foo"), []byte("bar"), []byte("baz")}, uint16(0)}, false},
+		{"valid", fields{uint32(123), []uint16{0, 1, 0, 1}, [][]byte{[]byte("foo"), []byte("bar"), []byte("baz")}, uint16(1)}, false},
 		{"invalid format code", fields{uint32(123), []uint16{2, 1, 0, 1}, [][]byte{[]byte("foo"), []byte("bar"), []byte("baz")}, uint16(0)}, true},
 		{"invalid result format code", fields{uint32(123), []uint16{1, 1, 0, 1}, [][]byte{[]byte("foo"), []byte("bar"), []byte("baz")}, uint16(2)}, true},
 	}
@@ -30,15 +31,32 @@ func TestFunctionCall_EncodeDecode(t *testing.T) {
 				ResultFormatCode: tt.fields.ResultFormatCode,
 			}
 			encoded := src.Encode([]byte{})
-			decoded := &FunctionCall{}
-			err := decoded.Decode(encoded[5:])
-			if (err != nil) != tt.wantErr {
-                t.Errorf("FunctionCall.Decode() error = %v, wantErr %v", err, tt.wantErr)
-                return
-            }
-			if diff := deep.Equal(src, decoded); diff != nil {
-				t.Error(diff)
+			dst := &FunctionCall{}
+			// Check the header
+			msgTypeCode := encoded[0]
+			if msgTypeCode != 'F' {
+				t.Errorf("msgTypeCode %v should be 'F'", msgTypeCode)
+				return
+			}
+			// Check length, does not include type code character
+			l := binary.BigEndian.Uint32(encoded[1:5])
+			if int(l) != (len(encoded) - 1) {
+				t.Errorf("Incorrect message length, got = %v, wanted = %v", l, len(encoded))
+			}
+			// Check decoding works as expected
+			err := dst.Decode(encoded[5:])
+			if err != nil {
+				if !tt.wantErr {
+					t.Errorf("FunctionCall.Decode() error = %v, wantErr %v", err, tt.wantErr)
+				}
+				return
+			}
+
+			if !reflect.DeepEqual(src, dst) {
+				t.Error("difference after encode / decode cycle")
+				t.Errorf("src = %v", src)
+				t.Errorf("dst = %v", dst)
 			}
 		})
 	}
-}
+}