Add test cases for PaginationPanel

src/test/java/seedu/address/ui/PaginationPanelTest.java

@@ -0,0 +1,44 @@
+package seedu.address.ui;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static seedu.address.testutil.Assert.assertThrows;
+
+import java.util.ArrayList;
+
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import javafx.collections.FXCollections;
+import javafx.collections.ObservableList;
+import javafx.embed.swing.JFXPanel;
+import seedu.address.model.contact.Contact;
+
+public class PaginationPanelTest {
+    @BeforeAll
+    public static void initJavaFxPlatform() {
+        new JFXPanel();
+    }
+
+    @Test
+    public void constructor_null_throwsNullPointerException() {
+        assertThrows(NullPointerException.class, () -> new PaginationPanel(null));
+    }
+
+    @Test
+    public void constructor_validObservationList_success() {
+        ObservableList<Contact> observableList = FXCollections.observableList(new ArrayList<>());
+        assertDoesNotThrow(() -> new PaginationPanel(observableList));
+    }
+
+    @Test
+    public void convertItemIndexToDisplayIndex_invalidIndex_throwsAssertionError() {
+        assertThrows(AssertionError.class, () -> PaginationPanel.convertItemIndexToDisplayIndex(-1));
+    }
+
+    @Test
+    public void convertItemIndexToDisplayIndex_validIndex_success() {
+        assertEquals(1, PaginationPanel.convertItemIndexToDisplayIndex(0));
+        assertEquals(10, PaginationPanel.convertItemIndexToDisplayIndex(9));
+    }
+}