basic, broken tests.

src/test/java/eu/simstadt/regionchooser/RegionChooserCommandLineInterfaceTest.java

+package eu.simstadt.regionchooser;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import java.io.PrintWriter;
+import java.io.StringWriter;
+import org.junit.jupiter.api.Test;
+import picocli.CommandLine;
+
+
+class RegionChooserCommandLineInterfaceTest
+{
+
+	@Test
+	void testCLIWithoutArgument() {
+		RegionChooserCommandLineInterface app = new RegionChooserCommandLineInterface();
+		CommandLine cmd = new CommandLine(app);
+
+		StringWriter sw = new StringWriter();
+		cmd.setOut(new PrintWriter(sw));
+
+		// black box testing
+		int exitCode = cmd.execute("--input=input.gml", "--output=output.gml", "--wkt=input.wkt");
+		assertEquals(0, exitCode);
+		assertEquals("Your output is abc...", sw.toString());
+	}
+
+}
+