dict: add update method

dictionary/dictionary.go

@@ -5,6 +5,7 @@ type Dictionary map[string]string
 const (
 	ErrNotFound         = DictionaryErr("could not find the word you were looking for")
 	ErrWordExists       = DictionaryErr("word exists")
+	ErrWordDoesNotExist = DictionaryErr("word does not exist")
 )
 
 type DictionaryErr string
@@ -34,3 +35,16 @@ func (d Dictionary) Add(word, definition string) error {
 	}
 	return nil
 }
+
+func (d Dictionary) Update(word, definition string) error {
+	_, err := d.Search(word)
+	switch err {
+	case ErrNotFound:
+		return ErrWordDoesNotExist
+	case nil:
+		d[word] = definition
+	default:
+		return err
+	}
+	return nil
+}

dictionary/dictionary_test.go

@@ -70,3 +70,24 @@ func TestAdd(t *testing.T) {
 		assertDefinition(t, dict, word, def)
 	})
 }
+
+func TestUpdate(t *testing.T) {
+	t.Run("update an existing word", func(t *testing.T) {
+		word := "test"
+		def := "this is just a test"
+		updated := "updated definition"
+		dict := Dictionary{word: def}
+
+		dict.Update(word, updated)
+		assertDefinition(t, dict, word, updated)
+	})
+
+	t.Run("update an non-existing word", func(t *testing.T) {
+		word := "test"
+		updated := "updated definition"
+		dict := Dictionary{}
+
+		err := dict.Update(word, updated)
+		assertError(t, err, ErrWordDoesNotExist)
+	})
+}