dict: add Add function and tests

dictionary/dictionary.go

@@ -13,3 +13,7 @@ func (d Dictionary) Search(word string) (string, error) {
 	}
 	return result, nil
 }
+
+func (d Dictionary) Add(word, definition string) {
+	d[word] = definition
+}

dictionary/dictionary_test.go

@@ -1,6 +1,8 @@
 package dictionary
 
-import "testing"
+import (
+	"testing"
+)
 
 func assertStrings(t testing.TB, got, want, given string) {
 	t.Helper()
@@ -36,3 +38,23 @@ func TestSearch(t *testing.T) {
 		assertError(t, err, ErrNotFound)
 	})
 }
+
+func assertDefinition(t testing.TB, dict Dictionary, word, def string) {
+	t.Helper()
+
+	got, err := dict.Search(word)
+	if err != nil {
+		t.Fatal("Should find added word:", err)
+	}
+	assertStrings(t, got, def, word)
+}
+
+func TestAdd(t *testing.T) {
+	dict := Dictionary{}
+
+	word := "test"
+	def := "this is just a test"
+
+	dict.Add(word, def)
+	assertDefinition(t, dict, word, def)
+}