Added basic test for the applied fix

tests/src/unit-consuming_stream.cpp

@@ -0,0 +1,126 @@
+
+
+
+#include "doctest_compatibility.h"
+
+#define JSON_TESTS_PRIVATE
+#include <nlohmann/json.hpp>
+using nlohmann::json;
+
+
+//This struct emulate an Input Stream, once a "char" is readed from it it is lost
+struct EmulateStream
+{
+    using difference_type = std::ptrdiff_t;
+    using value_type = char;
+    using pointer = const char*;
+    using reference = const char&;
+    using iterator_category = std::input_iterator_tag;
+
+    // Like a pop_left() -> consume one char from the underlying buffer
+    static char ConsumeChar(std::string* str)
+    {
+        const char c = str->front();
+        str->erase(0, 1);
+
+        return c;
+    }
+
+    EmulateStream()
+        :
+        target{nullptr}
+    {}
+
+    EmulateStream(std::string* target_)
+        :
+        target{target_},
+        c{ConsumeChar(target_)}
+    {}
+
+    EmulateStream& operator++()
+    {
+        c = ConsumeChar(target);
+
+        return *this;
+    }
+
+    bool operator!=(const EmulateStream& rhs) const
+    {
+        return rhs.target != target;
+    }
+
+    reference operator*() const
+    {
+        return c;
+    }
+
+    std::string* target;
+    char c;
+
+};
+
+EmulateStream CreateBegin(std::string& tgt)
+{
+    return EmulateStream{&tgt};
+}
+
+EmulateStream CreateEnd(const std::string& tgt)
+{
+    return {};
+}
+
+
+
+TEST_CASE("consume only needed")
+{
+
+    nlohmann::detail::json_sax_acceptor<json> sax_parser;
+
+    const std::string json_A = R"({ "key_A" : "value_A" })";
+    const std::string json_B = R"({ "key_B" : "value_B" })";
+
+    std::string json_concat_AB = json_A + json_B;
+
+    CHECK(
+        json::sax_parse(
+            CreateBegin(json_concat_AB),
+            CreateEnd(json_concat_AB),
+            &sax_parser,
+            nlohmann::detail::input_format_t::json,
+            false
+        )
+        == true
+    );
+
+
+    CHECK(json_concat_AB == json_B);
+
+
+    CHECK(
+        json::sax_parse(
+            CreateBegin(json_concat_AB),
+            CreateEnd(json_concat_AB),
+            &sax_parser,
+            nlohmann::detail::input_format_t::json,
+            false
+        )
+        == true
+    );
+
+
+    CHECK(json_concat_AB == "");
+    CHECK(json_concat_AB.size() == 0);
+
+
+    CHECK(
+        json::sax_parse(
+            CreateBegin(json_concat_AB),
+            CreateEnd(json_concat_AB),
+            &sax_parser,
+            nlohmann::detail::input_format_t::json,
+            false
+        )
+        == false
+    );
+
+}