Add unit tests var substitions

src/test/java/org/sonarsource/scanner/cli/PropertyResolverTest.java

@@ -104,6 +104,18 @@ public class PropertyResolverTest {
     assertThat(resolved.get("B")).isEqualTo("value b");
     assertThat(resolved.get("C")).isEqualTo("${A value b}");
   }
+  
+  @Test
+  public void missing_var() {
+    Map<String, String> env = new HashMap<>();
+    Properties map = new Properties();
+    map.put("A", "/path/$missing var/");
+    
+    PropertyResolver resolver = new PropertyResolver(map, env);
+    Properties resolved = resolver.resolve();
+    assertThat(resolved.get("A")).isEqualTo("/path/ var/");
+
+  }
 
   @Test
   public void fail_loop_properties_resolution() {