diff --git a/CMakeLists.txt b/CMakeLists.txt
index e73f25f..4e528d5 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -26,6 +26,14 @@ set(TEST_FILES
 
 add_executable(OMGL src/main.cpp ${SOURCE_FILES})
 
-# add_executable(Test tests/MainTest.cpp ${TEST_FILES} ${SOURCE_FILES})
+add_executable(Test tests/MainTest.cpp ${TEST_FILES} ${SOURCE_FILES})
 
-# target_link_libraries(Test ${GTEST_LIBRARIES} Threads::Threads)
+target_link_libraries(Test ${GTEST_LIBRARIES} Threads::Threads)
+
+add_custom_target(copy-files ALL
+        COMMAND ${CMAKE_COMMAND} -E copy_directory
+        ${CMAKE_SOURCE_DIR}/tests/programs/
+        ${CMAKE_BINARY_DIR}/programs
+        )
+
+add_dependencies(Test copy-files)
diff --git a/include/syntax_tree.hpp b/include/syntax_tree.hpp
index 106354b..d83b636 100644
--- a/include/syntax_tree.hpp
+++ b/include/syntax_tree.hpp
@@ -10,6 +10,9 @@ struct Variable;
 struct VariableInStack;
 struct Expression;
 
+void SetPrintStringStream();
+std::stringstream& GetPrintStringStream();
+
 struct Node {
   Node* parent = nullptr;
   Node* next = nullptr;
diff --git a/src/main.cpp b/src/main.cpp
index 0a5b4db..df7efca 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1,5 +1,6 @@
 #include <iostream>
 #include <fstream>
+#include <sstream>
 #include "preprocessor.hpp"
 #include "lexer.hpp"
 #include "syntax_tree.hpp"
@@ -12,7 +13,6 @@ int main(int argc, char* argv[]) {
     return 1;
   }
   std::ifstream fin(argv[1]);
-
   {
     std::string str;
     while (getline(fin, str)) {
diff --git a/src/syntax_tree.cpp b/src/syntax_tree.cpp
index 185b372..f6122fe 100644
--- a/src/syntax_tree.cpp
+++ b/src/syntax_tree.cpp
@@ -2,10 +2,32 @@
 #include <stdexcept>
 #include <limits>
 #include <iostream>
+#include <optional>
+#include <sstream>
 #include "syntax_tree.hpp"
 
 using Type = Lexer::LexerToken::Type;
 
+std::optional<std::stringstream> output_print;
+
+void SetPrintStringStream() {
+  output_print = std::stringstream();
+}
+
+std::stringstream& GetPrintStringStream() {
+  if (output_print) {
+    return *output_print;
+  }
+  throw std::logic_error("not string stream");
+}
+
+std::ostream& GetPrintOstream() {
+  if (output_print) {
+    return *output_print;
+  }
+  return std::cout;
+}
+
 bool IsOperation(Type type) {
   switch (type) {
     case Type::Equal:
@@ -651,12 +673,12 @@ void CallFunction::Run(std::vector<std::shared_ptr<VariableInStack>>& stack) {
     for (size_t i = 0; i < parameters.size(); ++i) {
       std::shared_ptr<VariableInStack>& t = *(stack.end() - parameters.size() + i);
       if (t->type_variable.id == TypeVariable::ID::type_int) {
-        std::cout << *((int*) t->memory) << " ";
+        GetPrintOstream() << *((int*) t->memory) << (i + 1 != parameters.size() ? " " : "");
       } else if (t->type_variable.id == TypeVariable::ID::type_string) {
-        std::cout << *((std::string*) t->memory) << " ";
+        GetPrintOstream() << *((std::string*) t->memory) << (i + 1 != parameters.size() ? " " : "");
       }
     }
-    std::cout << std::endl;
+    GetPrintOstream() << std::endl;
   }
 }
 
diff --git a/tests/MainTest.cpp b/tests/MainTest.cpp
index 83bd23c..99784e9 100644
--- a/tests/MainTest.cpp
+++ b/tests/MainTest.cpp
@@ -1,4 +1,46 @@
 #include <gtest/gtest.h>
+#include <iostream>
+#include <fstream>
+#include "preprocessor.hpp"
+#include "lexer.hpp"
+#include "syntax_tree.hpp"
+
+std::string LoadFile(const std::string& file) {
+  std::string program;
+  std::ifstream fin(file);
+  {
+    std::string str;
+    while (getline(fin, str)) {
+      str.push_back('\n');
+      program += str;
+    }
+  }
+  return program;
+}
+
+void RunTest(const std::string& program_file, const std::string& result_file) {
+  std::string program = LoadFile(program_file);
+  program = Preprocessor(std::move(program));
+  Lexer lexer;
+  lexer.ParseText(program);
+  auto tokens = lexer.GetTokens();
+  SyntaxTree tree;
+  tree.PushLexerTokenList(tokens);
+  tree.Compile();
+
+  SetPrintStringStream();
+  tree.Run();
+  std::string result = LoadFile(result_file);
+  ASSERT_EQ(result, GetPrintStringStream().str());
+}
+
+TEST(test_int, full_test) {
+  RunTest("programs/int/1.omgpl", "programs/int/1.res");
+}
+
+TEST(test_string, full_test) {
+  RunTest("programs/string/1.omgpl", "programs/string/1.res");
+}
 
 int main() {
   testing::InitGoogleTest();
diff --git a/tests/programs/int/1.omgpl b/tests/programs/int/1.omgpl
new file mode 100644
index 0000000..ca84f71
--- /dev/null
+++ b/tests/programs/int/1.omgpl
@@ -0,0 +1,13 @@
+int x = 0;
+for (int i = 0; i < 10; i += 1) {
+    x += i;
+}
+print(x);
+for (int i = 0; i < 10; i += 1) {
+    x -= i;
+}
+print(x);
+for (int i = 0; i < 4; i += 1) {
+    x = (x + 1) * i;
+}
+print(x);
\ No newline at end of file
diff --git a/tests/programs/int/1.res b/tests/programs/int/1.res
new file mode 100644
index 0000000..a60126d
--- /dev/null
+++ b/tests/programs/int/1.res
@@ -0,0 +1,3 @@
+45
+0
+15
diff --git a/tests/programs/string/1.omgpl b/tests/programs/string/1.omgpl
new file mode 100644
index 0000000..463fe6e
--- /dev/null
+++ b/tests/programs/string/1.omgpl
@@ -0,0 +1,11 @@
+string s = "";
+
+for (int i = 0; i < 10; i += 1) {
+    if ((i / 2) * 2 == i) {
+        s += "a";
+    }
+    if ((i / 2) * 2 != i) {
+        s += "b";
+    }
+}
+print(s);
\ No newline at end of file
diff --git a/tests/programs/string/1.res b/tests/programs/string/1.res
new file mode 100644
index 0000000..160610a
--- /dev/null
+++ b/tests/programs/string/1.res
@@ -0,0 +1 @@
+ababababab