test: Add basic unit tests for Main class

Co-authored-by: aider (ollama/qwen2.5-coder:14b-instruct) <aider@aider.chat>

src/test/java/puzzle/MainTest.java

@@ -0,0 +1,29 @@
+package puzzle;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class MainTest {
+
+    @Test
+    public void testGeneratePuzzle() {
+        // Arrange
+        var opts = new Main.Opts();
+        opts.seed = 1234;
+        opts.pop = 18;
+        opts.gens = 300;
+        opts.wordsPath = "src/test/resources/puzzle/pool.txt";
+        opts.minSimplicity = 0;
+        opts.threads = 1;
+        opts.tries = 1;
+
+        // Act
+        var result = Main.generatePuzzle(opts);
+
+        // Assert
+        assertNotNull(result);
+        assertNotNull(result.mask());
+        assertNotNull(result.filled());
+        assertTrue(result.filled().ok);
+    }
+}