System.assert(Blob.valueOf('abc') == Blob.valueOf('abc'));

private static Boolean eq(Blob b1, Blob b2) {
    if (b1.size() == b2.size()) {
        String s1 = EncodingUtil.base64Encode(b1);
        String s2 = EncodingUtil.base64Encode(b2);
        return s1 == s2;
    } else {
        return false;
    }
}