diff --git a/big-int/src/bigint.cpp b/big-int/src/bigint.cpp
index b16ca20..bf6456b 100644
--- a/big-int/src/bigint.cpp
+++ b/big-int/src/bigint.cpp
@@ -80,4 +80,4 @@ largeInt::largeInt(std::string nValue)
     }
     this->number = nValue;
 }
-} // namespace libbig
\ No newline at end of file
+} // namespace libbig
diff --git a/big-int/src/bigint.hpp b/big-int/src/bigint.hpp
index d2988a8..a9cb938 100644
--- a/big-int/src/bigint.hpp
+++ b/big-int/src/bigint.hpp
@@ -94,9 +94,9 @@ class largeInt
 
     //   POSTFIX OPERATORS
 
-    void operator=(largeInt);
-    void operator=(int);
-    void operator=(int64_t);
+    largeInt &operator=(const largeInt &);
+    largeInt &operator=(int);
+    largeInt &operator=(int64_t);
 
     bool operator==(const largeInt &);
     bool operator==(int);
@@ -123,7 +123,7 @@ class largeInt
     bool operator>=(int64_t);
 
     friend std::istream &operator>>(std::istream &, largeInt &);
-    friend std::ostream &operator<<(std::ostream &, largeInt &);
+    friend std::ostream &operator<<(std::ostream &, const largeInt &);
 };
 } // namespace libbig
 
diff --git a/big-int/src/operators/assignment_operator.cpp b/big-int/src/operators/assignment_operator.cpp
index f5c6018..9f64f77 100644
--- a/big-int/src/operators/assignment_operator.cpp
+++ b/big-int/src/operators/assignment_operator.cpp
@@ -28,9 +28,29 @@
 #include <istream>
 #include <ostream>
 
-#include "../bigint.hpp"
+#include <bigint.hpp>
 
 namespace libbig
 {
+largeInt &largeInt::operator=(const largeInt &x)
+{
+    sign = x.sign;
+    number = x.number;
+    return *this;
+}
+
+largeInt &largeInt::operator=(int x)
+{
+    sign = x >= 0;
+    number = std::to_string(std::abs(x));
+    return *this;
+}
+
+largeInt &largeInt::operator=(int64_t x)
+{
+    sign = x >= 0;
+    number = std::to_string(std::abs(x));
+    return *this;
+}
 
-} // namespace libbig
\ No newline at end of file
+} // namespace libbig
diff --git a/big-int/src/operators/ostream_operator.cpp b/big-int/src/operators/ostream_operator.cpp
index 4412449..3d6db5e 100644
--- a/big-int/src/operators/ostream_operator.cpp
+++ b/big-int/src/operators/ostream_operator.cpp
@@ -32,7 +32,7 @@
 
 namespace libbig
 {
-std::ostream &operator<<(std::ostream &out, largeInt &z)
+std::ostream &operator<<(std::ostream &out, const largeInt &z)
 {
     // checks if this->sign is negative, then inserts number in ostream
     if (z.sign == NEGATIVE)
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 6656470..2858ad9 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -1,3 +1,8 @@
+add_subdirectory(operators)
+add_subdirectory(operations)
+add_subdirectory(regex)
+add_subdirectory(big-int)
+
 enable_testing()
 file( GLOB TEST_SOURCES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} *.cpp )
 foreach(testsourcefile ${TEST_SOURCES})
@@ -5,7 +10,3 @@ foreach(testsourcefile ${TEST_SOURCES})
     add_executable( ${testname} ${testsourcefile} )
     target_link_libraries( ${testname} big-int )
 endforeach()
-
-add_subdirectory(operators)
-add_subdirectory(operations)
-add_subdirectory(big-int)
\ No newline at end of file
diff --git a/tests/operators/CMakeLists.txt b/tests/operators/CMakeLists.txt
index c1ee5d9..9ab7ea8 100644
--- a/tests/operators/CMakeLists.txt
+++ b/tests/operators/CMakeLists.txt
@@ -6,3 +6,5 @@ foreach(testsourcefile ${TEST_SOURCES})
     target_link_libraries( ${testname} big-int )
     add_test(${testname} ${testname})
 endforeach()
+
+file(COPY ${CMAKE_CURRENT_SOURCE_DIR}/input.txt DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/input.txt)
\ No newline at end of file
diff --git a/tests/operators/assignment_operator_test.cpp b/tests/operators/assignment_operator_test.cpp
new file mode 100644
index 0000000..99e7dfb
--- /dev/null
+++ b/tests/operators/assignment_operator_test.cpp
@@ -0,0 +1,49 @@
+/**
+ * Boost Software License - Version 1.0 - August 17th, 2003
+ * Permission is hereby granted, free of charge, to any person
+ * or organization obtaining a copy of the software and
+ * accompanying documentation covered by this license
+ * (the "Software") to use, reproduce, display, distribute,
+ * execute, and transmit the Software, and to prepare derivative
+ * works of the Software, and to permit third-parties to whom the
+ * Software is furnished to do so, all subject to the following:
+ *
+ * The copyright notices in the Software and this entire statement,
+ * including the above license grant, this restriction and the following
+ * disclaimer, must be included in all copies of the Software, in whole or
+ * in part, and all derivative works of the Software, unless such copies
+ * or derivative works are solely in the form of machine-executable
+ * object code generated by a source language processor.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, TITLE AND
+ * NON-INFRINGEMENT. IN NO EVENT SHALL THE COPYRIGHT HOLDERS OR ANYONE
+ * DISTRIBUTING THE SOFTWARE BE LIABLE FOR ANY DAMAGES OR OTHER LIABILITY,
+ * WHETHER IN CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+ * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+#include <bigint.hpp>
+#include <cassert>
+
+int main()
+{
+    libbig::largeInt a(20);
+    libbig::largeInt b = a;
+    assert(b == 20);
+    assert(b == a);
+
+    b = libbig::largeInt(-100000);
+    a = b;
+    assert(a == -100000);
+    assert(a == b);
+
+    b = libbig::largeInt("1000000000");
+    a = b;
+    assert(a == 1000000000);
+    assert(a == b);
+    
+    return 0;
+}
diff --git a/tests/operators/input.txt b/tests/operators/input.txt
new file mode 100644
index 0000000..2bcfa4b
--- /dev/null
+++ b/tests/operators/input.txt
@@ -0,0 +1,14 @@
+1
+100
+10000
+100000000
+10000000000000000
+100000000000000000000000000000000
+100000000000000000000000000000000000000000000000000000000000000000
+99999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
+1000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
+-10000000000000000000000000
+-1122178617862763873649236587264782365872467823
+-149023932491
+-34873298478923748973289476592365782689523657926958326459823659726598237503297598246583657924628934928357891
+-26589237985678256786763278562876389472836578264892365427961
\ No newline at end of file
diff --git a/tests/operators/ostream_test.cpp b/tests/operators/ostream_test.cpp
new file mode 100644
index 0000000..8e22244
--- /dev/null
+++ b/tests/operators/ostream_test.cpp
@@ -0,0 +1,30 @@
+#include <cassert>
+#include <fstream>
+#include <iostream>
+#include <sstream>
+
+#include <bigint.hpp>
+
+int main()
+{
+    libbig::largeInt a;
+    std::stringstream buffer;
+    std::ifstream f("input.txt");
+    std::string line;
+
+    if (f.is_open())
+    {
+        while (std::getline(f, line))
+        {
+            a = libbig::largeInt(line);
+            buffer << a;
+            assert(buffer.str().compare(std::string(line)) == 0);
+            buffer.str(std::string());
+        }
+        f.close();
+    } else {
+        throw std::runtime_error("Couldn't open input.txt");
+    }
+
+    return 0;
+}
diff --git a/tests/regex/CMakeLists.txt b/tests/regex/CMakeLists.txt
new file mode 100644
index 0000000..1cd7207
--- /dev/null
+++ b/tests/regex/CMakeLists.txt
@@ -0,0 +1,11 @@
+enable_testing()
+file( GLOB TEST_SOURCES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} *.cpp )
+foreach(testsourcefile ${TEST_SOURCES})
+    string ( REPLACE ".cpp" "" testname ${testsourcefile} )
+    add_executable( ${testname} ${testsourcefile} )
+    target_link_libraries( ${testname} big-int )
+    add_test(${testname} ${testname})
+endforeach()
+
+file(COPY ${CMAKE_CURRENT_SOURCE_DIR}/regex_accepted_input.txt DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/regex_accepted_input.txt)
+file(COPY ${CMAKE_CURRENT_SOURCE_DIR}/regex_rejected_input.txt DESTINATION ${CMAKE_CURRENT_BINARY_DIR}/regex_rejected_input.txt)
diff --git a/tests/regex/regex_accepted_input.txt b/tests/regex/regex_accepted_input.txt
new file mode 100644
index 0000000..04b50f7
--- /dev/null
+++ b/tests/regex/regex_accepted_input.txt
@@ -0,0 +1,9 @@
+0
+1
+-1
+-97946569
+27659857
+-436539467
+-43679760796362595017
+100000000000000000000000000000000000000000000000000000000000
+-100000000000000000000000000000000000000000000000000000000000
\ No newline at end of file
diff --git a/tests/regex/regex_rejected_input.txt b/tests/regex/regex_rejected_input.txt
new file mode 100644
index 0000000..3732713
--- /dev/null
+++ b/tests/regex/regex_rejected_input.txt
@@ -0,0 +1,8 @@
+--9
++6
++897497948
+98734h987ew
+$^%%*&^(*
+az928758
+1000000000000000000000000a0000000
+-1000000000000b000000000000000000
\ No newline at end of file
diff --git a/tests/regex/regex_test.cpp b/tests/regex/regex_test.cpp
new file mode 100644
index 0000000..aeda0d4
--- /dev/null
+++ b/tests/regex/regex_test.cpp
@@ -0,0 +1,32 @@
+#include <cassert>
+#include <iostream>
+#include <regex>
+#include <string>
+#include <fstream>
+#include <exception>
+
+int main() {
+    std::regex regExpr("(\\-)?(\\d)+");
+    std::string line;
+
+    std::ifstream f_accepted("regex_accepted_input.txt");
+    if (f_accepted.is_open()) {
+        while (std::getline(f_accepted, line)) {
+            assert(std::regex_match(line, regExpr) == true);
+        }
+        f_accepted.close();
+    } else {
+        throw std::runtime_error("Couldn't open regex_accepted_input.txt");
+    }
+
+    std::ifstream f_rejected("regex_rejected_input.txt");
+    if (f_rejected.is_open()) {
+        while (std::getline(f_rejected, line)) {
+            assert(std::regex_match(line, regExpr) == false);
+        }
+        f_rejected.close();
+    } else {
+        throw std::runtime_error("Couldn't open regex_rejected_input.txt");
+    }
+    return 0;
+}