Fix test compilation around pipeline processor (#3554)

## Summary
- allow tests to spy on PipelineProcessor web requests
- fix ResponseEntity usage in PipelineProcessorTest

## Testing
- `./gradlew test --offline` *(fails: No route to host while downloading
gradle-8.14-all.zip)*

src/test/java/stirling/software/SPDF/controller/api/pipeline/PipelineProcessorTest.java

@@ -0,0 +1,76 @@
+package stirling.software.SPDF.controller.api.pipeline;
+
+import static org.junit.jupiter.api.Assertions.*;
+import static org.mockito.ArgumentMatchers.*;
+import static org.mockito.Mockito.*;
+
+import java.util.List;
+import java.util.Map;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.core.io.ByteArrayResource;
+import org.springframework.core.io.Resource;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+
+import jakarta.servlet.ServletContext;
+
+import stirling.software.SPDF.model.PipelineConfig;
+import stirling.software.SPDF.model.PipelineOperation;
+import stirling.software.SPDF.model.PipelineResult;
+
+@ExtendWith(MockitoExtension.class)
+class PipelineProcessorTest {
+
+    @Mock
+    ApiDocService apiDocService;
+
+    @Mock
+    UserServiceInterface userService;
+
+    @Mock
+    ServletContext servletContext;
+
+    PipelineProcessor pipelineProcessor;
+
+    @BeforeEach
+    void setUp() {
+        pipelineProcessor = spy(new PipelineProcessor(apiDocService, userService, servletContext));
+    }
+
+    @Test
+    void runPipelineWithFilterSetsFlag() throws Exception {
+        PipelineOperation op = new PipelineOperation();
+        op.setOperation("filter-page-count");
+        op.setParameters(Map.of());
+        PipelineConfig config = new PipelineConfig();
+        config.setOperations(List.of(op));
+
+        Resource file = new ByteArrayResource("data".getBytes()) {
+            @Override
+            public String getFilename() {
+                return "test.pdf";
+            }
+        };
+
+        List<Resource> files = List.of(file);
+
+        when(apiDocService.isMultiInput("filter-page-count")).thenReturn(false);
+        when(apiDocService.getExtensionTypes(false, "filter-page-count")).thenReturn(List.of("pdf"));
+
+        doReturn(new ResponseEntity<>(new byte[0], HttpStatus.OK))
+                .when(pipelineProcessor)
+                .sendWebRequest(anyString(), any());
+
+        PipelineResult result = pipelineProcessor.runPipelineAgainstFiles(files, config);
+
+        assertTrue(result.isFiltersApplied(), "Filter flag should be true when operation filters file");
+        assertFalse(result.isHasErrors(), "No errors should occur");
+        assertTrue(result.getOutputFiles().isEmpty(), "Filtered file list should be empty");
+    }
+}
+