diff --git a/.gitignore b/.gitignore
index 54300f1..045b2f6 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,3 +2,5 @@
 /obj
 /lab01.depend
 /lab01.layout
+/unittest.depend
+/unittest.layout
diff --git a/histogram.cpp b/histogram.cpp
index f66701b..24e81b0 100644
--- a/histogram.cpp
+++ b/histogram.cpp
@@ -2,7 +2,7 @@
 
 using namespace std;
 
-static void
+void
 find_minmax(const vector<double>& numbers, double& min, double& max) {
     min = numbers[0];
     max = numbers[0];
diff --git a/histogram_internal.h b/histogram_internal.h
new file mode 100644
index 0000000..eb9cdfb
--- /dev/null
+++ b/histogram_internal.h
@@ -0,0 +1,5 @@
+#pragma once
+#include <vector>
+
+void
+find_minmax(const std::vector<double>& numbers, double& min, double& max);
diff --git a/lab01.cbp b/lab01.cbp
index b8887e3..bad2e84 100644
--- a/lab01.cbp
+++ b/lab01.cbp
@@ -37,6 +37,9 @@
 		<Unit filename="histogram.h">
 			<Option target="&lt;{~None~}&gt;" />
 		</Unit>
+		<Unit filename="histogram_internal.h">
+			<Option target="&lt;{~None~}&gt;" />
+		</Unit>
 		<Unit filename="main.cpp" />
 		<Unit filename="text.cpp" />
 		<Unit filename="text.h">
diff --git a/unittest.cbp b/unittest.cbp
new file mode 100644
index 0000000..bffa065
--- /dev/null
+++ b/unittest.cbp
@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="UTF-8" standalone="yes" ?>
+<CodeBlocks_project_file>
+	<FileVersion major="1" minor="6" />
+	<Project>
+		<Option title="unittest" />
+		<Option pch_mode="2" />
+		<Option compiler="gcc" />
+		<Build>
+			<Target title="Debug">
+				<Option output="bin/Debug/unittest" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Debug/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-g" />
+				</Compiler>
+			</Target>
+			<Target title="Release">
+				<Option output="bin/Release/unittest" prefix_auto="1" extension_auto="1" />
+				<Option object_output="obj/Release/" />
+				<Option type="1" />
+				<Option compiler="gcc" />
+				<Compiler>
+					<Add option="-O2" />
+				</Compiler>
+				<Linker>
+					<Add option="-s" />
+				</Linker>
+			</Target>
+		</Build>
+		<Compiler>
+			<Add option="-Wall" />
+		</Compiler>
+		<Unit filename="doctest.h">
+			<Option target="&lt;{~None~}&gt;" />
+		</Unit>
+		<Unit filename="histogram.cpp" />
+		<Unit filename="histogram_internal.h" />
+		<Unit filename="unittest.cpp" />
+		<Extensions>
+			<lib_finder disable_auto="1" />
+		</Extensions>
+	</Project>
+</CodeBlocks_project_file>
diff --git a/unittest.cpp b/unittest.cpp
new file mode 100644
index 0000000..a9ba7e5
--- /dev/null
+++ b/unittest.cpp
@@ -0,0 +1,12 @@
+#define DOCTEST_CONFIG_NO_MULTITHREADING
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+#include "doctest.h"
+#include "histogram_internal.h"
+
+TEST_CASE("distinct positive numbers") {
+    double min = 0;
+    double max = 0;
+    find_minmax({1, 2}, min, max);
+    CHECK(min == 1);
+    CHECK(max == 2);
+}