unvis: add some more error tests

These error cases were already handled correctly, but we really should
have tests for them anyway. Now that we have proper error variables
declared we can also test for specific errors as well.

Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>

pkg/govis/unvis_test.go

@@ -19,6 +19,7 @@
 package govis
 
 import (
+	"strconv"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -26,17 +27,33 @@ import (
 )
 
 func TestUnvisError(t *testing.T) {
-	for _, test := range []string{
-		// Octal escape codes allow you to specify invalid ASCII values.
-		"\\777",
-		"\\420\\322\\455",
-		"\\652\\233",
+	for _, test := range []struct {
+		input string
+		err   error
 	}{
-		t.Run(test, func(t *testing.T) {
-			_, err := Unvis(test, DefaultVisFlags)
-			require.Errorf(t, err, "invalid octal escape should give an error")
-			assert.ErrorContains(t, err, "escape base 8")
-			assert.ErrorContains(t, err, "outside latin-1 encoding")
+		// Octal escape codes allow you to specify invalid ASCII values.
+		{"\\777", errOutsideLatin1},
+		{"\\420\\322\\455", errOutsideLatin1},
+		{"\\652\\233", errOutsideLatin1},
+		// Escapes that end abruptly.
+		{"\\", errEndOfString},
+		{"\\J", errUnknownEscapeChar},
+		{"a bad slash: \\", errEndOfString},
+		{"testing -- \\x", errEndOfString},
+		{"\\xG0 test", strconv.ErrSyntax},
+		{"  abc \\Mx", errUnknownEscapeChar},
+		{"\\Mx", errUnknownEscapeChar},
+		{"\\M-", errEndOfString},
+		{"\\M-\u5000", errOutsideLatin1},
+		{"\\M^", errEndOfString},
+		{"\\^", errEndOfString},
+		{"\\^\u5000", errOutsideLatin1},
+		{"\\M", errEndOfString},
+	} {
+		t.Run(test.input, func(t *testing.T) {
+			_, err := Unvis(test.input, DefaultVisFlags)
+			require.Errorf(t, err, "invalid escape string should give an error")
+			assert.ErrorIs(t, err, test.err, "unexpected error from invalid escape string")
 		})
 	}
 }