add example characterization test (#28)

build.gradle.kts

@@ -14,6 +14,7 @@ dependencies {
     testImplementation("org.junit.jupiter:junit-jupiter")
     testImplementation("org.assertj:assertj-core:3.24.2")
     testImplementation("org.mockito:mockito-core:5.6.0")
+    testImplementation("com.approvaltests:approvaltests:22.2.0")
 }
 
 tasks.test {

src/test/java/org/example/ExampleCollaboratorTest.java

@@ -0,0 +1,21 @@
+package org.example;
+
+import org.approvaltests.combinations.CombinationApprovals;
+import org.junit.jupiter.api.Test;
+
+class ExampleCollaboratorTest {
+
+  @Test
+  void sum() {
+    CombinationApprovals.verifyAllCombinations(
+        this::doSum,
+        new Integer[] {-1, 2, 3, 4},
+        new Integer[] {-1, 2, 3, 4}
+    );
+  }
+
+  private int doSum(final Integer a, final Integer b) {
+    final ExampleCollaborator exampleCollaborator = new ExampleCollaborator();
+    return exampleCollaborator.sum(a, b);
+  }
+}

src/test/java/org/example/ExampleCollaboratorTest.sum.approved.txt

@@ -0,0 +1,16 @@
+[-1, -1] => -2 
+[-1, 2] => 1 
+[-1, 3] => 2 
+[-1, 4] => 3 
+[2, -1] => 1 
+[2, 2] => 4 
+[2, 3] => 5 
+[2, 4] => 6 
+[3, -1] => 2 
+[3, 2] => 5 
+[3, 3] => 6 
+[3, 4] => 7 
+[4, -1] => 3 
+[4, 2] => 6 
+[4, 3] => 7 
+[4, 4] => 8