tests: add more coverage for Lesson15

Signed-off-by: Anthony D. Mays <[email protected]>

Author: anthonydmays

lesson_15/tdd/tdd_app/src/test/java/com/codedifferently/lesson15/Lesson15Test.java

@@ -10,4 +10,10 @@ class Lesson15Test {
   public void testLesson15() {
     assertThat(new Lesson15()).isNotNull();
   }
+
+  @Test
+  public void testGetGreeting() {
+    // Act
+    Lesson15.main(null);
+  }
 }