(#171) Add puzzle for junit migration

pom.xml

@@ -147,6 +147,15 @@ OF THE POSSIBILITY OF SUCH DAMAGE.
       <optional>true</optional>
     </dependency>
     <dependency>
+      <!--
+      @todo #171:30m Migrate all simple tests to Junit 5. For the sake of
+       smaller PRs, migration can be done in steps
+       1) All tests classes without @Rule, and @Test(expected = ...)
+       2) All parameterized tests classes
+       3) The rest, (i.e dependent on @Rule's and so on)
+       After completing one of the steps, create a new puzzle for the next.
+       After all tests are run by Junit 5 remove this dependency.
+      -->
       <groupId>org.junit.vintage</groupId>
       <artifactId>junit-vintage-engine</artifactId>
       <version>${junit-platform.version}</version>