Introduce test utility class for files.

jplag.frontend-testutils/src/test/java/de/jplag/testutils/FileUtil.java

@@ -0,0 +1,42 @@
+package de.jplag.testutils;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.io.File;
+import java.util.Arrays;
+
+/**
+ * Test utility regarding files and directories.
+ */
+public final class FileUtil {
+
+    private static final String CONTENT_NOT_FOUND = "Directory contents not as expected";
+    private static final String DIRECTORY_NOT_FOUND = "Could not find directory: ";
+
+    private FileUtil() {
+        // private constructor to prevent instantiation
+    }
+
+    /**
+     * Checks if a directory exists and contains the expected files.
+     * @param directory is the directory to check.
+     * @param expectedFilesSorted is the sorted list (a to z) of expected file names.
+     */
+    public static void assertDirectory(File directory, String[] expectedFilesSorted) {
+        assertTrue(directory.exists(), DIRECTORY_NOT_FOUND + directory);
+        String[] filesInDirectory = directory.list();
+        Arrays.sort(filesInDirectory);
+        assertArrayEquals(expectedFilesSorted, filesInDirectory, CONTENT_NOT_FOUND);
+    }
+
+    /**
+     * Clears all files from a directory that whose names end in a certain suffix.
+     * @param directory is the target directory.
+     * @param suffix is the file suffix of the files to clear.
+     */
+    public static void clearFiles(File directory, String suffix) {
+        Arrays.stream(directory.listFiles()).filter(file -> file.getName().endsWith(suffix)).forEach(File::delete);
+    }
+
+}