diff --git a/test/base.hpp b/test/base.hpp
index 4e5aac2..3d82960 100644
--- a/test/base.hpp
+++ b/test/base.hpp
@@ -43,7 +43,7 @@ class Base
 {
 public:
   virtual ~Base() = default;
-  virtual void saySomething() = 0;
+  virtual std::string saySomething() = 0;
 };
 
 class BaseWithInterfaceCtor
diff --git a/test/global_plugins.cpp b/test/global_plugins.cpp
index 3c9865d..e47c7fb 100644
--- a/test/global_plugins.cpp
+++ b/test/global_plugins.cpp
@@ -30,7 +30,7 @@
  * 2020, Copied from plugins1.cpp and plugins2.cpp and changing class names
  */
 
-#include <iostream>
+#include <string>
 
 #include "class_loader/class_loader.hpp"
 
@@ -39,36 +39,36 @@
 class Kangaroo : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("[Angry growl]\n");
+    return "[Angry growl]";
   }
 };
 
 class Panda : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("[Excited squeaks!!!]\n");
+    return "[Excited squeaks!!!]";
   }
 };
 
 class Hyena : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("[Cackling laugh]\n");
+    return "[Cackling laugh]";
   }
 };
 
 class Alpaca : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("hhhaaaaaaaaaa\n");
+    return "hhhaaaaaaaaaa";
   }
 };
 
diff --git a/test/plugins1.cpp b/test/plugins1.cpp
index 5d4872d..7ba1b45 100644
--- a/test/plugins1.cpp
+++ b/test/plugins1.cpp
@@ -27,7 +27,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <iostream>
+#include <string>
 
 #include "class_loader/class_loader.hpp"
 
@@ -36,45 +36,45 @@
 class Dog : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("Bark\n");
+    return "Bark";
   }
 };
 
 class Cat : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("Meow\n");
+    return "Meow";
   }
 };
 
 class Duck : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("Quack\n");
+    return "Quack";
   }
 };
 
 class Cow : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("Moooo\n");
+    return "Moooo";
   }
 };
 
 class Sheep : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("Baaah\n");
+    return "Baaah";
   }
 };
 
diff --git a/test/plugins2.cpp b/test/plugins2.cpp
index 40a66f2..4b50403 100644
--- a/test/plugins2.cpp
+++ b/test/plugins2.cpp
@@ -27,7 +27,7 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#include <iostream>
+#include <string>
 
 #include "class_loader/class_loader.hpp"
 
@@ -36,36 +36,36 @@
 class Robot : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("Beep boop\n");
+    return "Beep boop";
   }
 };
 
 class Alien : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("Znornoff!!!\n");
+    return "Znornoff!!!";
   }
 };
 
 class Monster : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("BEAAAHHHH\n");
+    return "BEAAAHHHH";
   }
 };
 
 class Zombie : public Base
 {
 public:
-  void saySomething() override
+  std::string saySomething() override
   {
-    printf("Brains!!!\n");
+    return "Brains!!!";
   }
 };