test(export): add integration tests for descriptor and service file generation

- Validate proper descriptor generation for `Exporter` and `XMLExporter` implementations.
- Ensure service file creation for base contracts and absence for capability contracts.
- Expand coverage with stub classes for JSON and DDI exporters.

Author: poikilotherm

export/src/test/java/io/gdcc/spi/export/ExporterImplTest.java

@@ -0,0 +1,105 @@
+
+package io.gdcc.spi.export;
+
+import io.gdcc.spi.export.fixtures.StubDdiExporter;
+import io.gdcc.spi.export.fixtures.StubJsonExporter;
+import io.gdcc.spi.meta.descriptor.Descriptor;
+import io.gdcc.spi.meta.descriptor.DescriptorFormat;
+import org.junit.jupiter.api.Test;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+/**
+ * Verifies that the annotation processor generates correct descriptors and service files
+ * when compiling real Exporter SPI implementations.
+ *
+ * <p>The test implementation classes in this package are compiled with the processor on the
+ * classpath. The processor writes descriptors and service files into {@code target/test-classes/},
+ * which this test reads at runtime to verify correctness.</p>
+ */
+class ExporterImplTest {
+    
+    @Test
+    void generatesDescriptorAndServiceFileForBaseExporterImplementation() throws IOException {
+        Class<?> implClass = StubJsonExporter.class;
+        
+        Descriptor descriptor = readDescriptor(implClass);
+        assertNotNull(descriptor, "Descriptor should be generated for " + implClass);
+        
+        assertEquals(DescriptorFormat.transformClassName(implClass), descriptor.klass());
+        assertEquals(Exporter.class.getCanonicalName(), descriptor.kind());
+        assertEquals(Exporter.API_LEVEL, descriptor.contractLevel(Exporter.class.getCanonicalName()));
+        assertEquals(ExportDataProvider.API_LEVEL, descriptor.requiredProviderLevel(ExportDataProvider.class.getCanonicalName()));
+        
+        String serviceFile = readServiceFile(Exporter.class);
+        assertNotNull(serviceFile, "Service file should be generated for Exporter");
+        assertTrue(serviceFile.contains(DescriptorFormat.transformClassName(implClass)), "Service file should contain " + implClass);
+    }
+    
+    @Test
+    void generatesDescriptorWithBaseAndCapabilityForXmlExporterImplementation() throws IOException {
+        Class<?> implClass = StubDdiExporter.class;
+        
+        Descriptor descriptor = readDescriptor(implClass);
+        assertNotNull(descriptor, "Descriptor should be generated for " + implClass);
+        
+        assertEquals(DescriptorFormat.transformClassName(implClass), descriptor.klass());
+        assertEquals(Exporter.class.getCanonicalName(), descriptor.kind());
+        assertEquals(Exporter.API_LEVEL, descriptor.contractLevel(Exporter.class.getCanonicalName()));
+        assertEquals(XMLExporter.API_LEVEL, descriptor.contractLevel(XMLExporter.class.getCanonicalName()));
+        assertEquals(ExportDataProvider.API_LEVEL, descriptor.requiredProviderLevel(ExportDataProvider.class.getCanonicalName()));
+        
+        String serviceFile = readServiceFile(Exporter.class);
+        assertNotNull(serviceFile, "Service file should be generated for Exporter");
+        assertTrue(serviceFile.contains(DescriptorFormat.transformClassName(implClass)), "Service file should contain " + implClass);
+    }
+    
+    @Test
+    void doesNotGenerateServiceFileForXmlExporterCapability() {
+        String serviceFile = readServiceFile(XMLExporter.class);
+        assertNull(serviceFile, "Service file must never be generated for capability contract XMLExporter");
+    }
+    
+    @Test
+    void xmlExporterDefaultMediaTypeSatisfiesBaseContract() throws IOException {
+        // StubDdiExporter implements XMLExporter (which extends Exporter) and does NOT
+        // override getMediaType(). Because XMLExporter extends Exporter in the Java type
+        // hierarchy, the default on XMLExporter satisfies the abstract declaration on Exporter.
+        // If this were not the case, compilation would have failed and no descriptor would exist.
+        Class<?> implClass = StubDdiExporter.class;
+        
+        Descriptor descriptor = readDescriptor(implClass);
+        assertNotNull(descriptor, "Descriptor should exist, proving compilation succeeded without explicit getMediaType() override");
+    }
+    
+    // ── Helpers ─────────────────────────────────────────────────────────────────
+    
+    private Descriptor readDescriptor(Class implClass) throws IOException {
+        String resourcePath = DescriptorFormat.toPath(implClass);
+        try (InputStream is = getClass().getClassLoader().getResourceAsStream(resourcePath)) {
+            if (is == null) {
+                return null;
+            }
+            return DescriptorFormat.read(new String(is.readAllBytes(), StandardCharsets.UTF_8));
+        }
+    }
+    
+    private String readServiceFile(Class<?> serviceType) {
+        String resourcePath = "META-INF/services/" + serviceType.getName();
+        try (InputStream is = getClass().getClassLoader().getResourceAsStream(resourcePath)) {
+            if (is == null) {
+                return null;
+            }
+            return new String(is.readAllBytes(), StandardCharsets.UTF_8);
+        } catch (IOException e) {
+            return null;
+        }
+    }
+}

export/src/test/java/io/gdcc/spi/export/fixtures/StubDdiExporter.java

@@ -0,0 +1,57 @@
+package io.gdcc.spi.export.fixtures;
+
+import io.gdcc.spi.export.ExportDataProvider;
+import io.gdcc.spi.export.XMLExporter;
+import io.gdcc.spi.meta.annotations.DataversePlugin;
+
+import java.io.OutputStream;
+import java.util.Locale;
+
+/**
+ * Minimal XMLExporter implementation for processor integration testing.
+ *
+ * <p>Does NOT override {@code getMediaType()} — the default from {@link XMLExporter}
+ * satisfies the abstract declaration on {@link io.gdcc.spi.export.Exporter} because XMLExporter extends Exporter.</p>
+ */
+@DataversePlugin
+public class StubDdiExporter implements XMLExporter {
+    @Override
+    public void exportDataset(ExportDataProvider dataProvider, OutputStream outputStream) {
+        /* Intentionally left blank for test class */
+    }
+
+    @Override
+    public String getFormatName() {
+        return "stub-ddi";
+    }
+
+    @Override
+    public String getDisplayName(Locale locale) {
+        return "Stub DDI";
+    }
+
+    @Override
+    public Boolean isHarvestable() {
+        return true;
+    }
+
+    @Override
+    public Boolean isAvailableToUsers() {
+        return true;
+    }
+
+    @Override
+    public String getXMLNameSpace() {
+        return "ddi:codebook:2_5";
+    }
+
+    @Override
+    public String getXMLSchemaLocation() {
+        return "https://ddialliance.org/Specification/DDI-Codebook/2.5/XMLSchema/codebook.xsd";
+    }
+
+    @Override
+    public String getXMLSchemaVersion() {
+        return "2.5";
+    }
+}

export/src/test/java/io/gdcc/spi/export/fixtures/StubJsonExporter.java

@@ -0,0 +1,44 @@
+package io.gdcc.spi.export.fixtures;
+
+import io.gdcc.spi.export.ExportDataProvider;
+import io.gdcc.spi.export.Exporter;
+import io.gdcc.spi.meta.annotations.DataversePlugin;
+
+import java.io.OutputStream;
+import java.util.Locale;
+
+/**
+ * Minimal base-only Exporter implementation for processor integration testing.
+ */
+@DataversePlugin
+public class StubJsonExporter implements Exporter {
+    @Override
+    public void exportDataset(ExportDataProvider dataProvider, OutputStream outputStream) {
+        /* Intentionally left blank for test class */
+    }
+
+    @Override
+    public String getFormatName() {
+        return "stub-json";
+    }
+
+    @Override
+    public String getDisplayName(Locale locale) {
+        return "Stub JSON";
+    }
+
+    @Override
+    public Boolean isHarvestable() {
+        return false;
+    }
+
+    @Override
+    public Boolean isAvailableToUsers() {
+        return true;
+    }
+
+    @Override
+    public String getMediaType() {
+        return "application/json";
+    }
+}