Add proper tests for execute-around pattern

execute-around/src/test/java/com/iluwatar/execute/around/SimpleFileWriterTest.java

@@ -0,0 +1,75 @@
+package com.iluwatar.execute.around;
+
+import org.junit.Assert;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Date: 12/12/15 - 3:21 PM
+ *
+ * @author Jeroen Meulemeester
+ */
+public class SimpleFileWriterTest {
+
+  /**
+   * Create a temporary folder, used to generate files in during this test
+   */
+  @Rule
+  public final TemporaryFolder testFolder = new TemporaryFolder();
+
+  /**
+   * Verify if the given writer is not 'null'
+   */
+  @Test
+  public void testWriterNotNull() throws Exception {
+    final File temporaryFile = this.testFolder.newFile();
+    new SimpleFileWriter(temporaryFile.getPath(), Assert::assertNotNull);
+  }
+
+  /**
+   * Test if the {@link SimpleFileWriter} creates a file if it doesn't exist
+   */
+  @Test
+  public void testNonExistentFile() throws Exception {
+    final File nonExistingFile = new File(this.testFolder.getRoot(), "non-existing-file");
+    assertFalse(nonExistingFile.exists());
+
+    new SimpleFileWriter(nonExistingFile.getPath(), Assert::assertNotNull);
+    assertTrue(nonExistingFile.exists());
+  }
+
+  /**
+   * Test if the data written to the file writer actually gets in the file
+   */
+  @Test
+  public void testActualWrite() throws Exception {
+    final String testMessage = "Test message";
+
+    final File temporaryFile = this.testFolder.newFile();
+    assertTrue(temporaryFile.exists());
+
+    new SimpleFileWriter(temporaryFile.getPath(), writer -> writer.write(testMessage));
+    assertTrue(Files.lines(temporaryFile.toPath()).allMatch(testMessage::equals));
+  }
+
+  /**
+   * Verify if an {@link IOException} during the write ripples through
+   */
+  @Test(expected = IOException.class)
+  public void testIOException() throws Exception {
+    final File temporaryFile = this.testFolder.newFile();
+    new SimpleFileWriter(temporaryFile.getPath(), writer -> {
+      throw new IOException("");
+    });
+  }
+
+}