code: пункты 5-6

project/histogram.cpp

@@ -2,7 +2,7 @@
 #include <vector>
 #include "histogram.h"
 using namespace std;
-static void
+void
 find_minmax(vector<double> numbers, double& min, double& max) {
     min = numbers[0];
     max = numbers[0];

unittest.cpp

@@ -0,0 +1,16 @@
+#define DOCTEST_CONFIG_NO_MULTITHREADING
+#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
+#include "doctest.h"
+#include "project\histogram_internal.h"
+
+TEST_CASE("distinct positive numbers") {
+    double min = 0;
+    double max = 0;
+    std::vector<double>v{2,1};
+    CHECK(v.size() != 0);
+    CHECK(v.size() != 1);
+    find_minmax({1, 2}, min, max);
+    CHECK(min == 1);
+    CHECK(max == 2);
+    CHECK(min != max);
+}