add java 7 predicate example

Author: daggerok

gradle/junit.gradle

@@ -2,6 +2,7 @@ allprojects {
   // read more: https://docs.gradle.org/4.6/release-notes.html#junit-5-support
 
   dependencies {
+    testImplementation 'org.assertj:assertj-core:3.10.0'
     testImplementation "junit:junit:$junit4Version"
     testImplementation "org.hamcrest:hamcrest-core:$hamcrestVersion"
     testImplementation "org.junit.jupiter:junit-jupiter-api:$junitJupiterVersion"

pom.xml

@@ -60,6 +60,13 @@
       <version>1.2.3</version>
     </dependency>
 
+    <!-- assertj -->
+    <dependency>
+      <groupId>org.assertj</groupId>
+      <artifactId>assertj-core</artifactId>
+      <version>3.10.0</version>
+      <scope>test</scope>
+    </dependency>
     <!-- junit 4 -->
     <dependency>
       <groupId>junit</groupId>

src/main/java/daggerok/java7/predicate/Java7Predicate.java

@@ -1,4 +1,42 @@
 package daggerok.java7.predicate;
 
+import lombok.RequiredArgsConstructor;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static java.util.Objects.nonNull;
+
 public class Java7Predicate {
+
+    public interface MyPredicate {
+        boolean test(final String value);
+    }
+
+    @RequiredArgsConstructor
+    public static class Is implements MyPredicate {
+        final String value;
+
+        @Override
+        public boolean test(String value) {
+            return value != null && value.contains(this.value);
+        }
+    }
+
+    public static class IsRed implements MyPredicate {
+        @Override
+        public boolean test(final String value) {
+            return nonNull(value) && value.toLowerCase().contains("red");
+        }
+    }
+
+    public static void sideEffect(final MyPredicate predicate) {
+        final List<String> list = Arrays.asList("ololo", "trololo", "red", "blue", "green", "red devil");
+        for (String i : list) {
+            if (predicate.test(i)) {
+                System.out.println("i = " + i);
+            }
+        }
+    }
 }

src/test/java/daggerok/AppJUnit5Test.java

@@ -0,0 +1,31 @@
+package daggerok.java7.predicate;
+
+import daggerok.extensions.CaptureSystemOutput;
+import lombok.extern.slf4j.Slf4j;
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import static daggerok.java7.predicate.Java7Predicate.sideEffect;
+import static org.junit.jupiter.api.Assertions.*;
+
+@Slf4j
+@CaptureSystemOutput
+@DisplayName("test predicate API: java 7")
+class Java7PredicateTest {
+
+    @Test
+    @DisplayName("test positive")
+    void testPredicate(final CaptureSystemOutput.OutputCapture outputCapture) {
+
+        assertAll(() -> {
+
+            sideEffect(new Java7Predicate.IsRed());
+            Assertions.assertThat(outputCapture.toString())
+                    .contains("i = red", "i = red devil");
+
+            sideEffect(new Java7Predicate.Is("green"));
+            Assertions.assertThat(outputCapture.toString().contains("t = green"));
+        });
+    }
+}