create seperate header for the splitter, move splitter tests to different cpp file

test/test_splitter.cpp

@@ -0,0 +1,43 @@
+#include <iostream>
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+#include "../include/ss/splitter.hpp"
+#include "doctest.h"
+#include <algorithm>
+
+TEST_CASE("testing splitter with escaping") {
+    std::vector<std::string> values{"10",   "he\\\"llo",
+                                    "\\\"", "\\\"a\\,a\\\"",
+                                    "3.33", "a\\\""};
+
+    char buff[128];
+    // with quote
+    ss::splitter<ss::quote<'"'>, ss::escape<'\\'>> s;
+    std::string delim = ",";
+    for (size_t i = 0; i < values.size() * values.size(); ++i) {
+        std::string input1;
+        std::string input2;
+        for (size_t j = 0; j < values.size(); ++j) {
+            if (i & (1 << j) && j != 2 && j != 3) {
+                input1.append(values[j]);
+                input2.append(values.at(values.size() - 1 - j));
+            } else {
+                input1.append("\"" + values[j] + "\"");
+                input2.append("\"" + values.at(values.size() - 1 - j) + "\"");
+            }
+            input1.append(delim);
+            input2.append(delim);
+        }
+        input1.pop_back();
+        input2.pop_back();
+        input1.append("\0\"");
+        input2.append("\0\"");
+
+        memcpy(buff, input1.c_str(), input1.size() + 1);
+        auto tup1 = s.split(buff, delim);
+        CHECK(tup1.size() == 6);
+
+        memcpy(buff, input2.c_str(), input2.size() + 1);
+        auto tup2 = s.split(buff, delim);
+        CHECK(tup2.size() == 6);
+    }
+}