ident: implement system identifier

Signed-off-by: Yonah <contrib@gensokyo.uk>

ident/ident_test.go

@@ -0,0 +1,101 @@
+package ident_test
+
+import (
+	"encoding"
+	"encoding/base64"
+	"fmt"
+	"reflect"
+	"testing"
+
+	"git.gensokyo.uk/cofront/cof-spec/ident"
+)
+
+// rTestCases describes multiple representation test cases.
+type rTestCases[V any, S interface {
+	encoding.TextMarshaler
+	encoding.TextUnmarshaler
+	fmt.Stringer
+
+	*V
+}] []struct {
+	name  string
+	ident V
+	want  []byte
+	err   error
+}
+
+// checkRepresentation runs tests described by testCases.
+func (testCases rTestCases[V, S]) run(t *testing.T) {
+	t.Helper()
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Helper()
+			t.Parallel()
+
+			t.Run("decode", func(t *testing.T) {
+				t.Helper()
+				t.Parallel()
+
+				var got V
+				if err := S(&got).UnmarshalText(tc.want); !reflect.DeepEqual(err, tc.err) {
+					t.Fatalf("UnmarshalText: error = %v, want %v", err, tc.err)
+				}
+
+				if tc.err != nil {
+					return
+				}
+
+				if !reflect.DeepEqual(got, tc.ident) {
+					t.Errorf("UnmarshalText: %#v, want %#v", got, tc.ident)
+				}
+			})
+
+			if tc.err != nil {
+				return
+			}
+
+			t.Run("encode", func(t *testing.T) {
+				t.Helper()
+				t.Parallel()
+
+				if got, err := S(&tc.ident).MarshalText(); err != nil {
+					t.Fatalf("MarshalText: error = %v", err)
+				} else if string(got) != string(tc.want) {
+					raw, decodeErr := base64.URLEncoding.AppendDecode(nil, got)
+					t.Logf("AppendDecode: %#v, error = %v", raw, decodeErr)
+
+					t.Errorf("MarshalText: %#v, want %#v", got, tc.want)
+				}
+
+				if got := S(&tc.ident).String(); got != string(tc.want) {
+					t.Errorf("String: %#v, want %#v", []byte(got), tc.want)
+				}
+			})
+		})
+	}
+}
+
+func TestErrors(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name string
+		err  error
+		want string
+	}{
+		{"UnexpectedSizeError", &ident.UnexpectedSizeError{
+			Data: make([]byte, 1<<10),
+			Want: ident.EncodedSizeSystem,
+		}, "got 1024 bytes for a 32-byte identifier"},
+	}
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			if got := tc.err.Error(); got != tc.want {
+				t.Errorf("Error: %q, want %q", got, tc.want)
+			}
+		})
+	}
+}