Bug fix UI crash when url is unrechable (#1642)

* feat: Add URL  reachability check in ConvertWebsiteToPDF

* Add tests for URL reachability in ConvertWebsiteToPdfTest

* test: Update URL in ConvertWebsiteToPdfTest for testing

src/test/java/stirling/software/SPDF/controller/api/converters/ConvertWebsiteToPdfTest.java

@@ -0,0 +1,41 @@
+package stirling.software.SPDF.controller.api.converters;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.http.ResponseEntity;
+
+import stirling.software.SPDF.model.api.converters.UrlToPdfRequest;
+import static org.junit.jupiter.api.Assertions.*;
+
+public class ConvertWebsiteToPdfTest {
+    @Test
+    public void test_exemption_is_thrown_when_invalid_url_format_provided() {
+
+        String invalid_format_Url = "invalid-url";
+        // Arrange
+        ConvertWebsiteToPDF convertWebsiteToPDF = new ConvertWebsiteToPDF();
+        UrlToPdfRequest request = new UrlToPdfRequest();
+        request.setUrlInput(invalid_format_Url);
+        // Act
+        IllegalArgumentException thrown = assertThrows(IllegalArgumentException.class, () -> {
+            convertWebsiteToPDF.urlToPdf(request);
+        });
+        // Assert
+        assertEquals("Invalid URL format provided.", thrown.getMessage());
+    }
+
+    @Test
+    public void test_exemption_is_thrown_when_url_is_not_reachable() {
+
+        String unreachable_Url = "https://www.googleeeexyz.com";
+        // Arrange
+        ConvertWebsiteToPDF convertWebsiteToPDF = new ConvertWebsiteToPDF();
+        UrlToPdfRequest request = new UrlToPdfRequest();
+        request.setUrlInput(unreachable_Url);
+        // Act
+        IllegalArgumentException thrown = assertThrows(IllegalArgumentException.class, () -> {
+            convertWebsiteToPDF.urlToPdf(request);
+        });
+        // Assert
+        assertEquals("URL is not reachable, please provide a valid URL.", thrown.getMessage());
+    }
+}