diff --git a/main.cpp b/main.cpp
index 469de2f..c18236c 100644
--- a/main.cpp
+++ b/main.cpp
@@ -1,5 +1,8 @@
 #include <iostream>
 #include <vector>
+#include "histogram.h"
+#include "text.h"
+#include "svg.h"
 using namespace std;
 
 struct Input {
@@ -26,92 +29,11 @@ input_data() {
     return in;
 }
 
-void
-find_minmax(const vector<double>& numbers, double& min, double& max) {
-    min = numbers[0];
-    max = numbers[0];
-
-    for (double x : numbers) {
-        if (x < min) {
-            min = x;
-        } else if (x > max) {
-            max = x;
-        }
-    }
-}
-
-vector<size_t>
-make_histogram(const vector<double>& numbers, size_t bin_count) {
-    vector<size_t> bins(bin_count, 0);
-
-    double min, max;
-    find_minmax(numbers, min, max);
-
-    double bin_size = (max - min) / bin_count;
-    if (bin_size == 0) {
-        bin_size = 1;
-    }
-
-    for (size_t i = 0; i < numbers.size(); i++) {
-        bool found = false;
-        for (size_t j = 0; (j < bin_count - 1) && !found; j++) {
-            auto lo = min + j * bin_size;
-            auto hi = min + (j + 1) * bin_size;
-            if ((lo <= numbers[i]) && (numbers[i] < hi)) {
-                bins[j]++;
-                found = true;
-            }
-        }
-        if (!found) {
-            bins[bin_count - 1]++;
-        }
-    }
-
-    return bins;
-}
-
-void
-show_histogram_text(const vector<size_t>& bins, size_t screen_width = 80) {
-    const size_t MAX_ASTERISK = screen_width - 3 - 1;
-
-    size_t max_count = 0;
-    for (size_t count : bins) {
-        if (count > max_count) {
-            max_count = count;
-        }
-    }
-
-    for (size_t i = 0; i < bins.size(); i++) {
-        size_t height = 0;
-
-        if (max_count > MAX_ASTERISK) {
-            height = static_cast<size_t>(
-                MAX_ASTERISK * static_cast<double>(bins[i]) / max_count
-            );
-        } else {
-            height = bins[i];
-        }
-
-        if (bins[i] < 10) {
-            cout << "  " << bins[i] << "|";
-        } else if (bins[i] < 100) {
-            cout << " " << bins[i] << "|";
-        } else {
-            cout << bins[i] << "|";
-        }
-
-        for (size_t j = 0; j < height; j++) {
-            cout << "*";
-        }
-        cout << endl;
-    }
-}
-
 int
 main() {
     auto in = input_data();
     auto bins = make_histogram(in.numbers, in.bin_count);
-    show_histogram_text(bins);
+    show_histogram_svg(bins);
 
     return 0;
 }
diff --git a/svg.cpp b/svg.cpp
new file mode 100644
index 0000000..a3fe7b7
--- /dev/null
+++ b/svg.cpp
@@ -0,0 +1,58 @@
+#include <iostream>
+#include <vector>
+#include <string>
+
+using namespace std;
+
+void svg_begin(double width, double height) {
+    cout << "<?xml version='1.0' encoding='UTF-8'?>\n";
+    cout << "<svg ";
+    cout << "width='" << width << "' ";
+    cout << "height='" << height << "' ";
+    cout << "viewBox='0 0 " << width << " " << height << "' ";
+    cout << "xmlns='http://www.w3.org/2000/svg'>\n";
+}
+
+void svg_end() {
+    cout << "</svg>\n";
+}
+
+void svg_text(double left, double baseline, const string& text) {
+    cout << "<text x='" << left << "' y='" << baseline << "'>" << text << "</text>\n";
+}
+
+void svg_rect(double x, double y, double width, double height,
+              string stroke = "black", string fill = "black") {
+    cout << "<rect x='" << x << "' y='" << y
+         << "' width='" << width << "' height='" << height
+         << "' stroke='" << stroke << "' fill='" << fill << "' />\n";
+}
+
+void show_histogram_svg(const vector<size_t>& bins) {
+    const auto IMAGE_WIDTH = 400;
+    const auto IMAGE_HEIGHT = 300;
+    const auto TEXT_LEFT = 20;
+    const auto TEXT_BASELINE = 20;
+    const auto TEXT_WIDTH = 50;
+    const auto BIN_HEIGHT = 30;
+
+    svg_begin(IMAGE_WIDTH, IMAGE_HEIGHT);
+
+    double top = 0;
+    size_t max_bin = 0;
+    for (size_t i = 0; i < bins.size(); ++i) {
+        if (bins[i] > max_bin) {
+            max_bin = bins[i];
+        }
+    }
+    double scale = (max_bin > 0) ? (IMAGE_WIDTH - TEXT_WIDTH) * 1.0 / max_bin : 0;
+
+    for (size_t bin : bins) {
+        const double bin_width = scale * bin;
+        svg_text(TEXT_LEFT, top + TEXT_BASELINE, to_string(bin));
+        svg_rect(TEXT_WIDTH, top, bin_width, BIN_HEIGHT);
+        top += BIN_HEIGHT;
+    }
+
+    svg_end();
+}
diff --git a/svg.h b/svg.h
new file mode 100644
index 0000000..0414e7e
--- /dev/null
+++ b/svg.h
@@ -0,0 +1,10 @@
+#ifndef SVG_H_INCLUDED
+#define SVG_H_INCLUDED
+
+#include <vector>
+
+void svg_begin(double width, double height);
+void svg_end();
+void show_histogram_svg(const std::vector<size_t>& bins);
+
+#endif // SVG_H_INCLUDED
diff --git a/unittest.cpp b/unittest.cpp
new file mode 100644
index 0000000..b951593
--- /dev/null
+++ b/unittest.cpp
@@ -0,0 +1,36 @@
+#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);
+}
+
+TEST_CASE("find_minmax with one element") {
+    std::vector<double> numbers{42};
+    double min, max;
+    find_minmax(numbers, min, max);
+    CHECK(min == 42);
+    CHECK(max == 42);
+}
+
+TEST_CASE("find_minmax with negative values") {
+    std::vector<double> numbers{-10.5, -2.3, -3.3};
+    double min, max;
+    find_minmax(numbers, min, max);
+    CHECK(min == -10.5);
+    CHECK(max == -2.3);
+}
+
+TEST_CASE("find_minmax with identical elements") {
+    std::vector<double> numbers{7, 7, 7, 7};
+    double min, max;
+    find_minmax(numbers, min, max);
+    CHECK(min == 7);
+    CHECK(max == 7);
+}