Add tests to check when a language is added several times

- Test that verifies that a language added twice is counted only once
- Test that proves that a language added 2 times is correctly deleted

Author: ValMati

exercises/concept/karls-languages/.meta/config.json

@@ -2,6 +2,9 @@
   "authors": [
     "jmrunkle"
   ],
+  "contributors": [
+    "Valmati"
+  ],
   "files": {
     "solution": [
       "src/main/java/LanguageList.java"

exercises/concept/karls-languages/.meta/src/reference/java/LanguageList.java

@@ -9,7 +9,9 @@ public boolean isEmpty() {
     }
 
     public void addLanguage(String language) {
-        languages.add(language);
+        if (!containsLanguage(language)) {
+            languages.add(language)
+        }
     }
 
     public void removeLanguage(String language) {

exercises/concept/karls-languages/src/test/java/LanguageListTest.java

@@ -34,6 +34,17 @@ public void removeLanguage() {
         assertThat(languageList.isEmpty()).isTrue();
     }
 
+    @Test
+    @Tag("task:3")
+    @DisplayName("The removeLanguage method correctly removes a language from the list that has been added twice")
+    public void removeLanguageTwice() {
+        languageList.addLanguage("Python");
+        languageList.addLanguage("Python");
+        languageList.removeLanguage("Python");
+
+        assertThat(languageList.isEmpty()).isTrue();
+    }
+
     @Test
     @Tag("task:4")
     @DisplayName("The firstLanguage method returns the first language that was added to the list")
@@ -56,6 +67,16 @@ public void countThree() {
         assertThat(languageList.count()).isEqualTo(3);
     }
 
+    @Test
+    @Tag("task:5")
+    @DisplayName("The count method returns 1 when the same language has been added twice")
+    public void countOne() {
+        languageList.addLanguage("Python");
+        languageList.addLanguage("Python");
+
+        assertThat(languageList.count()).isEqualTo(1);
+    }
+
     @Test
     @Tag("task:5")
     @DisplayName("The count method returns 0 when the list is empty")