diff --git a/simulator/kernel/mars/t/unit_test.cpp b/simulator/kernel/mars/t/unit_test.cpp
index d3309ae9c..8313333f5 100644
--- a/simulator/kernel/mars/t/unit_test.cpp
+++ b/simulator/kernel/mars/t/unit_test.cpp
@@ -38,7 +38,7 @@ struct System
     std::shared_ptr<Simulator> sim = nullptr;
     std::shared_ptr<Kernel> mars_kernel = nullptr;
     std::shared_ptr<FuncMemory> mem = nullptr;
-    
+
     template<typename ... KernelArgs>
     explicit System( KernelArgs&&... args)
         : sim( Simulator::create_simulator( "mips64", true))
@@ -236,7 +236,78 @@ TEST_CASE( "MARS: open non existing file")
     CHECK( sys.sim->read_cpu_register( v0) == all_ones<uint64>());
 }
 
-TEST_CASE( "MARS: open, write, read and close a file")
+static Trap write_buff_to_file( System* sys, uint64 descr,
+                                uint64 buff_ptr, uint64 chars_to_write)
+{
+    sys->sim->write_cpu_register( v0, 15u); //write to file
+    sys->sim->write_cpu_register( a0, descr);
+    sys->sim->write_cpu_register( a1, buff_ptr);
+    sys->sim->write_cpu_register( a2, chars_to_write);
+    return sys->mars_kernel->execute();
+}
+
+static Trap open_file( System* sys, uint64 filename_ptr, uint64 flags)
+{
+    sys->sim->write_cpu_register( v0, 13u); // open file
+    sys->sim->write_cpu_register( a0, filename_ptr);
+    sys->sim->write_cpu_register( a1, flags);
+    return sys->mars_kernel->execute();
+}
+
+static Trap read_from_file( System* sys, uint64 descr,
+                            uint64 buff_ptr, uint64 chars_to_read)
+{
+    sys->sim->write_cpu_register( v0, 14u); // read from file
+    sys->sim->write_cpu_register( a0, descr);
+    sys->sim->write_cpu_register( a1, buff_ptr);
+    sys->sim->write_cpu_register( a2, chars_to_read);
+    return sys->mars_kernel->execute();
+}
+
+static Trap close_file( System* sys, uint64 descr)
+{
+    sys->sim->write_cpu_register( v0, 16u);
+    sys->sim->write_cpu_register( a0, descr);
+    return sys->mars_kernel->execute();
+}
+
+TEST_CASE( "MARS: open and close a file")
+{
+    std::string filename( "tempfile");
+    std::ostringstream output;
+    System sys( std::cin, output);
+    sys.mem->write_string( filename, 0x1000);
+
+    auto trap = open_file( &sys, 0x1000, 1); // WRONLY
+    auto descr = sys.sim->read_cpu_register( v0);
+    CHECK( trap == Trap::NO_TRAP);
+    CHECK( descr >= 3);
+
+    trap = close_file ( &sys, descr);
+    CHECK( trap == Trap::NO_TRAP);
+}
+
+TEST_CASE( "MARS: open, write and close file")
+{
+    std::string filename( "tempfile");
+    std::ostringstream output;
+    System sys( std::cin, output);
+    sys.mem->write_string( filename, 0x1000);
+    sys.mem->write_string( "Lorem Ipsum\n", 0x2000);
+
+    auto trap = open_file( &sys, 0x1000, 1); // WRONLY
+    auto descr = sys.sim->read_cpu_register( v0);
+    CHECK( trap == Trap::NO_TRAP);
+    CHECK( descr >= 3);
+
+    trap = write_buff_to_file( &sys, descr, 0x2000, 11);
+    CHECK( trap == Trap::NO_TRAP); // FIXME(pkryukov): Can file be checked by read()
+
+    trap = close_file ( &sys, descr);
+    CHECK( trap == Trap::NO_TRAP);
+}
+
+TEST_CASE( "MARS: open, read and close a file")
 {
     std::string filename("tempfile");
     std::ostringstream output;
@@ -244,57 +315,37 @@ TEST_CASE( "MARS: open, write, read and close a file")
     sys.mem->write_string( filename, 0x1000);
     sys.mem->write_string( "Lorem Ipsum\n", 0x2000);
 
-    sys.sim->write_cpu_register( v0, 13u); // open file
-    sys.sim->write_cpu_register( a0, 0x1000u);
-    sys.sim->write_cpu_register( a1, 1); // write
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
+    auto trap = open_file( &sys, 0x1000, 1); // open WRONLY
     auto descriptor = sys.sim->read_cpu_register( v0);
+    CHECK( trap == Trap::NO_TRAP);
     CHECK( descriptor >= 3);
+    trap = write_buff_to_file( &sys, descriptor, 0x2000, 11);
+    CHECK( trap == Trap::NO_TRAP);
 
-    sys.sim->write_cpu_register( v0, 15u); // write to file
-    sys.sim->write_cpu_register( a0, descriptor);
-    sys.sim->write_cpu_register( a1, 0x2000);
-    sys.sim->write_cpu_register( a2, 11);
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
+    trap = close_file( &sys, descriptor);
+    CHECK( trap == Trap::NO_TRAP);
 
-    sys.sim->write_cpu_register( v0, 16u); // close file
-    sys.sim->write_cpu_register( a0, descriptor);
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
-
-    sys.sim->write_cpu_register( v0, 13u); // open file
-    sys.sim->write_cpu_register( a0, 0x1000u);
-    sys.sim->write_cpu_register( a1, 9); // append
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
+    trap = open_file( &sys, 0x1000, 9); // open O_APPEND
     descriptor = sys.sim->read_cpu_register( v0);
+    CHECK( trap == Trap::NO_TRAP);
     CHECK( descriptor >= 3);
+    trap = write_buff_to_file( &sys, descriptor, 0x2000, 11);
+    CHECK( trap == Trap::NO_TRAP);
 
-    sys.sim->write_cpu_register( v0, 15u); // write to file
-    sys.sim->write_cpu_register( a0, descriptor);
-    sys.sim->write_cpu_register( a1, 0x2000);
-    sys.sim->write_cpu_register( a2, 11);
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
+    trap = close_file( &sys, descriptor);
+    CHECK( trap == Trap::NO_TRAP);
 
-    sys.sim->write_cpu_register( v0, 16u); // close file
-    sys.sim->write_cpu_register( a0, descriptor);
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
-
-    sys.sim->write_cpu_register( v0, 13u); // open file
-    sys.sim->write_cpu_register( a0, 0x1000u);
-    sys.sim->write_cpu_register( a1, 0); // read
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
+    trap = open_file( &sys, 0x1000, 0); // read
     descriptor = sys.sim->read_cpu_register( v0);
+    CHECK( trap == Trap::NO_TRAP);
     CHECK( descriptor >= 3);
+    trap = read_from_file( &sys, descriptor, 0x3000, 22);
+    CHECK( trap == Trap::NO_TRAP);
 
-    sys.sim->write_cpu_register( v0, 14u); // read from file
-    sys.sim->write_cpu_register( a0, descriptor);
-    sys.sim->write_cpu_register( a1, 0x3000);
-    sys.sim->write_cpu_register( a2, 22);
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
     CHECK( sys.mem->read_string( 0x3000) == "Lorem IpsumLorem Ipsum");
 
-    sys.sim->write_cpu_register( v0, 16u); // close file
-    sys.sim->write_cpu_register( a0, descriptor);
-    CHECK( sys.mars_kernel->execute() == Trap::NO_TRAP);
+    trap = close_file( &sys, descriptor);
+    CHECK( trap == Trap::NO_TRAP);
 }
 
 TEST_CASE( "MARS: open file with invalid mode")
@@ -342,7 +393,7 @@ TEST_CASE( "MARS: close error")
     CHECK( mars_kernel->execute() == Trap::NO_TRAP);
 }
 
-TEST_CASE( "MARS: exit with code") 
+TEST_CASE( "MARS: exit with code")
 {
     auto sim = Simulator::create_simulator ("mips64", true);
     auto mars_kernel = create_mars_kernel( );
@@ -354,7 +405,7 @@ TEST_CASE( "MARS: exit with code")
     CHECK( mars_kernel->get_exit_code() == 21u);
 }
 
-TEST_CASE( "MARS: unsupported syscall") 
+TEST_CASE( "MARS: unsupported syscall")
 {
     auto sim = Simulator::create_simulator ("mips64", true);
     auto mars_kernel = create_mars_kernel( );