Working helloworld with test

.gitignore

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+target
+.idea

pom.xml

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+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+ 
+  <groupId>eu.mateuszpiela.helloworld</groupId>
+  <artifactId>helloworld</artifactId>
+  <version>1.0-SNAPSHOT</version>
+ 
+  <name>helloworld</name>
+  <url>https://mateuszpiela.eu</url>
+ 
+  <properties>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <maven.compiler.source>17</maven.compiler.source>
+    <maven.compiler.target>17</maven.compiler.target>
+  </properties>
+ 
+  <dependencies>
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <version>4.13.2</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+ 
+  <build>
+    <plugins>
+        <plugin>
+            <groupId>org.apache.maven.plugins</groupId>
+            <artifactId>maven-jar-plugin</artifactId>
+            <version>3.3.0</version>
+            <configuration>
+            <archive>
+                <index>true</index>
+                <manifest>
+                    <addClasspath>true</addClasspath>
+                    <mainClass>eu.mateuszpiela.helloworld.Main</mainClass>
+                </manifest>
+            </archive>
+            </configuration>
+        </plugin>
+      </plugins>
+  </build>
+</project>

src/main/java/eu/mateuszpiela/helloworld/Main.java

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+package eu.mateuszpiela.helloworld;
+
+public class Main {
+    public static void main(String[] args) {
+
+        System.out.println("Hello world from java");
+    }
+}

src/test/java/eu/mateuszpiela/helloworld/MainTest.java

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+package eu.mateuszpiela.helloworld;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+import java.lang.reflect.Array;
+
+import static org.junit.Assert.assertEquals;
+
+public class MainTest {
+    private final ByteArrayOutputStream outContent = new ByteArrayOutputStream();
+    private final ByteArrayOutputStream errContent = new ByteArrayOutputStream();
+    private final PrintStream originalOut = System.out;
+    private final PrintStream originalErr = System.err;
+
+    @Before
+    public void setUpStreams() {
+        System.setOut(new PrintStream(outContent));
+        System.setErr(new PrintStream(errContent));
+    }
+
+    @Test
+    public void AssertConsoleOutputIsHelloWorld() {
+        String[] args = {};
+        eu.mateuszpiela.helloworld.Main.main(args);
+        assertEquals("Hello world from java" + System.lineSeparator(), outContent.toString());
+    }
+
+    @After
+    public void restoreStreams() {
+        System.setOut(originalOut);
+        System.setErr(originalErr);
+    }
+}