Adds unit testing examples with JUnit and AssertJ

Adds recursive function implementation of showList

Author: micwypych

.gitignore

@@ -22,3 +22,6 @@
 hs_err_pid*
 .gradle
 build/
+
+#intelij
+.idea

build.gradle

@@ -23,4 +23,5 @@ repositories {
 // In this section you declare the dependencies for your production and test code
 dependencies {
     testCompile 'junit:junit:4.12'
+    testCompile 'org.assertj:assertj-core:3.8.0'
 }

gradle/wrapper/gradle-wrapper.properties

@@ -1,6 +1,6 @@
-#Wed May 24 17:28:23 CEST 2017
+#Thu Jun 01 17:55:03 CEST 2017
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-3.5-bin.zip
+distributionUrl=https\://services.gradle.org/distributions/gradle-3.5-all.zip

src/main/java/recursion/ListUtility.java

@@ -0,0 +1,25 @@
+package recursion;
+
+import java.util.Arrays;
+
+/**
+ * Created by mwypych on 01.06.17.
+ */
+public class ListUtility {
+
+    public static String showList(Integer[] number) {
+        if (number.length == 0) {
+            return "";
+        }
+        return head(number) + showList(tail(number));
+    }
+
+    public static <T> T head(T[] list) {
+        return list[0];
+    }
+
+    public static <T> T[] tail(T[] list) {
+        return Arrays.copyOfRange(list, 1, list.length);
+    }
+
+}

src/main/java/unittesting/UtilityFactorial.java

@@ -0,0 +1,16 @@
+package unittesting;
+
+/**
+ * Created by mwypych on 01.06.17.
+ */
+public class UtilityFactorial {
+    public static int factorial(int value) {
+        if (value < 0) {
+            throw new IllegalArgumentException("value cannot be less than 0");
+        }
+        if (value == 0) {
+            return 1;
+        }
+        return value * factorial(value-1);
+    }
+}

src/test/java/unittesting/UtilityFactorialAssertJTest.java

@@ -0,0 +1,34 @@
+package unittesting;
+
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static unittesting.UtilityFactorial.factorial;
+
+/**
+ * Created by mwypych on 01.06.17.
+ */
+public class UtilityFactorialAssertJTest {
+    @Test
+    public void factorialOfNegativeThrowsAnException() {
+        assertThatExceptionOfType(IllegalArgumentException.class).isThrownBy(() -> {
+            factorial(-20);
+        });
+    }
+
+    @Test
+    public void factorialOfZeroIsOne() {
+        assertThat(factorial(0)).isEqualTo(1);
+    }
+
+    @Test
+    public void factorialOfOneIsOne() {
+        assertThat(factorial(1)).isEqualTo(1);
+    }
+
+    @Test
+    public void factorialOfNineIs362880() {
+        assertThat(factorial(9)).isEqualTo(362880);
+    }
+}

src/test/java/unittesting/UtilityFactorialJUnitTest.java

@@ -0,0 +1,42 @@
+package unittesting;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
+
+import static org.junit.Assert.assertEquals;
+import static unittesting.UtilityFactorial.factorial;
+
+/**
+ * Created by mwypych on 01.06.17.
+ */
+public class UtilityFactorialJUnitTest {
+    @Rule
+    public ExpectedException thrown = ExpectedException.none();
+
+    @Test(expected = IllegalArgumentException.class)
+    public void factorialOfNegativeThrowsAnException__1() {
+        factorial(-20);
+    }
+
+    @Test
+    public void factorialOfNegativeThrowsAnException__2() {
+        thrown.expect(IllegalArgumentException.class);
+        factorial(-20);
+    }
+
+    @Test
+    public void factorialOfZeroIsOne() {
+        assertEquals("factorial(0)", 1, factorial(0));
+    }
+
+    @Test
+    public void factorialOfOneIsOne() {
+        assertEquals("factorial(1)", 1, factorial(1));
+    }
+
+    @Test
+    public void factorialOfNineIs362880() {
+        assertEquals("factorial(9)", 362880, factorial(9));
+    }
+}