Code to insert SGR formatting into already formatted strings

tools/tui/sgr/insert-formatting_test.go

@@ -0,0 +1,31 @@
+// License: GPLv3 Copyright: 2023, Kovid Goyal, <kovid at kovidgoyal.net>
+
+package sgr
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+var _ = fmt.Print
+
+func TestInsertFormatting(t *testing.T) {
+	test := func(src, expected string, spans ...*Span) {
+		actual := InsertFormatting(src, spans...)
+		if diff := cmp.Diff(expected, actual); diff != "" {
+			t.Fatalf("Failed with %#v:\n%#v != %#v\n%s", src, expected, actual, diff)
+		}
+	}
+	test(
+		"\x1b[44m abcd \x1b[49m",
+		"\x1b[44m a\x1b[33;41mbc\x1b[39;49m\x1b[44md \x1b[49m",
+		NewSpan(2, 2).SetForeground(3).SetBackground(1),
+	)
+	test(
+		"abcd",
+		"a\x1b[92mbcd\x1b[39m",
+		NewSpan(1, 11).SetForeground(10),
+	)
+}