fs: add IsSet convenience method to Bits

fs/bits.go

@@ -114,6 +114,11 @@ func (b *Bits[C]) Set(s string) error {
 	return nil
 }
 
+// IsSet returns true all the bits in mask are set in b.
+func (b Bits[C]) IsSet(mask Bits[C]) bool {
+	return (b & mask) == mask
+}
+
 // Type of the value.
 //
 // If C has a Type() string method then it will be used instead.

fs/bits_test.go

@@ -80,6 +80,15 @@ func TestBitsSet(t *testing.T) {
 	}
 }
 
+func TestBitsIsSet(t *testing.T) {
+	b := bitA | bitB
+	assert.True(t, b.IsSet(bitA))
+	assert.True(t, b.IsSet(bitB))
+	assert.True(t, b.IsSet(bitA|bitB))
+	assert.False(t, b.IsSet(bitC))
+	assert.False(t, b.IsSet(bitA|bitC))
+}
+
 func TestBitsType(t *testing.T) {
 	f := bits(0)
 	assert.Equal(t, "Bits", f.Type())