bytes, strings: add ContainsFunc

Fixes #54386.

Change-Id: I78747da337ed6129e4f7426dd0483a644bed82e3
Reviewed-on: https://go-review.googlesource.com/c/go/+/460216
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Run-TryBot: hopehook <hopehook@golangcn.org>
Auto-Submit: Ian Lance Taylor <iant@golang.org>

1 files changed, 11 insertions, 0 deletions

diff --git a/src/bytes/bytes_test.go b/src/bytes/bytes_test.go
index fc2824485a..05c0090b61 100644
--- a/src/bytes/bytes_test.go
+++ b/src/bytes/bytes_test.go
@@ -1847,6 +1847,17 @@ func TestContainsRune(t *testing.T) {
 	}
 }
 
+func TestContainsFunc(t *testing.T) {
+	for _, ct := range ContainsRuneTests {
+		if ContainsFunc(ct.b, func(r rune) bool {
+			return ct.r == r
+		}) != ct.expected {
+			t.Errorf("ContainsFunc(%q, func(%q)) = %v, want %v",
+				ct.b, ct.r, !ct.expected, ct.expected)
+		}
+	}
+}
+
 var makeFieldsInput = func() []byte {
 	x := make([]byte, 1<<20)
 	// Input is ~10% space, ~10% 2-byte UTF-8, rest ASCII non-space.