diff --git a/test/test_entity-manager.cpp b/test/test_entity-manager.cpp
new file mode 100644
index 0000000..653a982
--- /dev/null
+++ b/test/test_entity-manager.cpp
@@ -0,0 +1,141 @@
+#include "Utils.hpp"
+
+#include <boost/container/flat_map.hpp>
+#include <nlohmann/json.hpp>
+#include <variant>
+
+#include "gtest/gtest.h"
+
+TEST(TemplateCharReplace, replaceOneInt)
+{
+    nlohmann::json j = {{"foo", "$bus"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["BUS"] = 23;
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = 23;
+    EXPECT_EQ(expected, j["foo"]);
+}
+
+TEST(TemplateCharReplace, replaceOneStr)
+{
+    nlohmann::json j = {{"foo", "$TEST"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = std::string("Test");
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "Test";
+    EXPECT_EQ(expected, j["foo"]);
+}
+
+TEST(TemplateCharReplace, replaceSecondStr)
+{
+    nlohmann::json j = {{"foo", "the $TEST"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = std::string("Test");
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "the Test";
+    EXPECT_EQ(expected, j["foo"]);
+}
+
+/*
+TODO This should work
+
+TEST(TemplateCharReplace, replaceMiddleStr)
+{
+    nlohmann::json j = {{"foo", "the $TEST worked"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = std::string("Test");
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "the Test worked";
+    EXPECT_EQ(expected, j["foo"]);
+}
+*/
+
+TEST(TemplateCharReplace, replaceLastStr)
+{
+    nlohmann::json j = {{"foo", "the Test $TEST"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = 23;
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "the Test 23";
+    EXPECT_EQ(expected, j["foo"]);
+}
+
+TEST(TemplateCharReplace, increment)
+{
+    nlohmann::json j = {{"foo", "3 plus 1 equals $TEST + 1"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = 3;
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "3 plus 1 equals 4";
+    EXPECT_EQ(expected, j["foo"]);
+}
+
+TEST(TemplateCharReplace, decrement)
+{
+    nlohmann::json j = {{"foo", "3 minus 1 equals $TEST - 1 !"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = 3;
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "3 minus 1 equals 2 !";
+    EXPECT_EQ(expected, j["foo"]);
+}
+
+TEST(TemplateCharReplace, modulus)
+{
+    nlohmann::json j = {{"foo", "3 mod 2 equals $TEST % 2"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = 3;
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "3 mod 2 equals 1";
+    EXPECT_EQ(expected, j["foo"]);
+}
+
+TEST(TemplateCharReplace, multiply)
+{
+    nlohmann::json j = {{"foo", "3 * 2 equals $TEST * 2"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = 3;
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "3 * 2 equals 6";
+    EXPECT_EQ(expected, j["foo"]);
+}
+
+TEST(TemplateCharReplace, divide)
+{
+    nlohmann::json j = {{"foo", "4 / 2 equals $TEST / 2"}};
+    auto it = j.begin();
+    boost::container::flat_map<std::string, BasicVariantType> data;
+    data["TEST"] = 4;
+
+    templateCharReplace(it, data, 0);
+
+    nlohmann::json expected = "4 / 2 equals 2";
+    EXPECT_EQ(expected, j["foo"]);
+}
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