objectionary#3236 add tests

eo-maven-plugin/src/test/java/org/eolang/maven/DownloadJnaMojoTest.java

@@ -1,16 +1,40 @@
 package org.eolang.maven;
 
+import java.io.IOException;
+import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.Paths;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
 class DownloadJnaMojoTest {
+
+    private static final Path OUT = Paths.get("target/classes");
+
+    private static final String JNA_JAR = "jna-5.14.0.jar";
+
     @Test
     void executesWithoutErrors(@TempDir final Path temp) {
         Assertions.assertDoesNotThrow(
             () -> new FakeMaven(temp).execute(DownloadJnaMojo.class),
             "Exception shouldn't been thrown"
         );
     }
-}
+
+    @Test
+    void createsOutDir(@TempDir final Path temp) throws IOException {
+        new FakeMaven(temp).execute(DownloadJnaMojo.class);
+        Assertions.assertTrue(
+            Files.exists(temp.resolve(OUT))
+        );
+    }
+
+    @Test
+    void downloadsCorrectly(@TempDir final Path temp) throws IOException {
+        new FakeMaven(temp).execute(DownloadJnaMojo.class);
+        Assertions.assertTrue(
+            Files.exists(temp.resolve(OUT).resolve(JNA_JAR))
+        );
+    }
+}