diff --git a/core/processor/pom.xml b/core/processor/pom.xml
index 8427a552eb841..aee2ce4090171 100644
--- a/core/processor/pom.xml
+++ b/core/processor/pom.xml
@@ -59,6 +59,17 @@
             <artifactId>jboss-logmanager</artifactId>
             <scope>test</scope> 
         </dependency>
+        <dependency>
+            <groupId>com.karuslabs</groupId>
+            <artifactId>elementary</artifactId>
+            <version>2.0.1</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>io.quarkus</groupId>
+            <artifactId>quarkus-builder</artifactId>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
diff --git a/core/processor/src/main/java/io/quarkus/annotation/processor/ExtensionAnnotationProcessor.java b/core/processor/src/main/java/io/quarkus/annotation/processor/ExtensionAnnotationProcessor.java
index c660290a11c37..3d978555bbecc 100644
--- a/core/processor/src/main/java/io/quarkus/annotation/processor/ExtensionAnnotationProcessor.java
+++ b/core/processor/src/main/java/io/quarkus/annotation/processor/ExtensionAnnotationProcessor.java
@@ -183,7 +183,7 @@ void doFinish() {
         Properties javaDocProperties = new Properties();
 
         try {
-            Files.walkFileTree(path, new FileVisitor<Path>() {
+            Files.walkFileTree(path, new FileVisitor<>() {
                 public FileVisitResult preVisitDirectory(final Path dir, final BasicFileAttributes attrs) {
                     return FileVisitResult.CONTINUE;
                 }
@@ -282,8 +282,6 @@ public FileVisitResult postVisitDirectory(final Path dir, final IOException exc)
         } catch (IOException e) {
             processingEnv.getMessager()
                     .printMessage(Diagnostic.Kind.ERROR, "Failed to generate extension doc: " + e);
-            return;
-
         }
     }
 
@@ -368,8 +366,7 @@ private void processBuildStep(RoundEnvironment roundEnv, TypeElement annotation)
                                     StandardLocation.SOURCE_OUTPUT,
                                     pkg.getQualifiedName()
                                             .toString(),
-                                    rbn.toString() + ".bsc",
-                                    clazz);
+                                    rbn + ".bsc", clazz);
                     writeResourceFile(binaryName, itemResource);
                 } catch (IOException e1) {
                     processingEnv.getMessager()
@@ -618,7 +615,7 @@ private void processMethodConfigMapping(ExecutableElement method, Properties jav
             if (method.getSimpleName()
                     .contentEquals("toString")
                     && method.getParameters()
-                            .size() == 0) {
+                            .isEmpty()) {
                 return;
             }
 
@@ -650,7 +647,7 @@ private TypeElement unwrapConfigGroup(TypeMirror typeMirror) {
         String name = declaredType.asElement()
                 .toString();
         List<? extends TypeMirror> typeArguments = declaredType.getTypeArguments();
-        if (typeArguments.size() == 0) {
+        if (typeArguments.isEmpty()) {
             if (!name.startsWith("java.")) {
                 return (TypeElement) declaredType.asElement();
             }
diff --git a/core/processor/src/test/java/io/quarkus/annotation/processor/ExtensionAnnotationProcessorTest.java b/core/processor/src/test/java/io/quarkus/annotation/processor/ExtensionAnnotationProcessorTest.java
new file mode 100644
index 0000000000000..d9d85a19ab53a
--- /dev/null
+++ b/core/processor/src/test/java/io/quarkus/annotation/processor/ExtensionAnnotationProcessorTest.java
@@ -0,0 +1,76 @@
+package io.quarkus.annotation.processor;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.util.List;
+
+import javax.tools.JavaFileObject;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import com.karuslabs.elementary.Results;
+import com.karuslabs.elementary.junit.JavacExtension;
+import com.karuslabs.elementary.junit.annotations.Classpath;
+import com.karuslabs.elementary.junit.annotations.Processors;
+
+import io.quarkus.annotation.processor.fs.CustomMemoryFileSystemProvider;
+
+@ExtendWith(JavacExtension.class)
+@Processors({ ExtensionAnnotationProcessor.class })
+class ExtensionAnnotationProcessorTest {
+
+    @BeforeEach
+    void beforeEach() {
+        // This is of limited use, since the filesystem doesn't seem to directly generate files, in the current usage
+        CustomMemoryFileSystemProvider.reset();
+    }
+
+    @Test
+    @Classpath("org.acme.examples.ClassWithBuildStep")
+    void shouldProcessClassWithBuildStepWithoutErrors(Results results) throws IOException {
+        assertNoErrrors(results);
+    }
+
+    @Test
+    @Classpath("org.acme.examples.ClassWithBuildStep")
+    void shouldGenerateABscFile(Results results) throws IOException {
+        assertNoErrrors(results);
+        List<JavaFileObject> sources = results.sources;
+        JavaFileObject bscFile = sources.stream()
+                .filter(source -> source.getName()
+                        .endsWith(".bsc"))
+                .findAny()
+                .orElse(null);
+        assertNotNull(bscFile);
+
+        String contents = removeLineBreaks(new String(bscFile
+                .openInputStream()
+                .readAllBytes(), StandardCharsets.UTF_8));
+        assertEquals("org.acme.examples.ClassWithBuildStep", contents);
+    }
+
+    private String removeLineBreaks(String s) {
+        return s.replace(System.getProperty("line.separator"), "")
+                .replace("\n", "");
+    }
+
+    @Test
+    @Classpath("org.acme.examples.ClassWithoutBuildStep")
+    void shouldProcessEmptyClassWithoutErrors(Results results) {
+        assertNoErrrors(results);
+    }
+
+    private static void assertNoErrrors(Results results) {
+        assertEquals(0, results.find()
+                .errors()
+                .count(),
+                "Errors were: " + results.find()
+                        .errors()
+                        .diagnostics());
+    }
+}
diff --git a/core/processor/src/test/java/io/quarkus/annotation/processor/fs/CustomMemoryFileSystem.java b/core/processor/src/test/java/io/quarkus/annotation/processor/fs/CustomMemoryFileSystem.java
new file mode 100644
index 0000000000000..432bd86b334e9
--- /dev/null
+++ b/core/processor/src/test/java/io/quarkus/annotation/processor/fs/CustomMemoryFileSystem.java
@@ -0,0 +1,158 @@
+package io.quarkus.annotation.processor.fs;
+
+import java.io.IOException;
+import java.net.URI;
+import java.nio.ByteBuffer;
+import java.nio.channels.SeekableByteChannel;
+import java.nio.file.FileStore;
+import java.nio.file.FileSystem;
+import java.nio.file.Path;
+import java.nio.file.PathMatcher;
+import java.nio.file.Paths;
+import java.nio.file.WatchService;
+import java.nio.file.attribute.UserPrincipalLookupService;
+import java.nio.file.spi.FileSystemProvider;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+public class CustomMemoryFileSystem extends FileSystem {
+
+    private final Map<URI, ByteBuffer> fileContents = new HashMap<>();
+    private final CustomMemoryFileSystemProvider provider;
+
+    public CustomMemoryFileSystem(CustomMemoryFileSystemProvider provider) {
+        this.provider = provider;
+    }
+
+    @Override
+    public FileSystemProvider provider() {
+        return provider;
+    }
+
+    @Override
+    public void close() throws IOException {
+        // No resources to close
+    }
+
+    @Override
+    public boolean isOpen() {
+        return true; // Always open
+    }
+
+    @Override
+    public boolean isReadOnly() {
+        return false; // This filesystem is writable
+    }
+
+    @Override
+    public String getSeparator() {
+        return "/"; // Unix-style separator
+    }
+
+    @Override
+    public Iterable<Path> getRootDirectories() {
+        return Collections.singleton(Paths.get("/")); // Single root directory
+    }
+
+    @Override
+    public Iterable<FileStore> getFileStores() {
+        return Collections.emptyList(); // No file stores
+    }
+
+    @Override
+    public Set<String> supportedFileAttributeViews() {
+        return Collections.emptySet(); // No supported file attribute views
+    }
+
+    @Override
+    public Path getPath(String first, String... more) {
+        String path = first;
+        for (String segment : more) {
+            path += "/" + segment;
+        }
+        return Paths.get(path);
+    }
+
+    @Override
+    public PathMatcher getPathMatcher(String syntaxAndPattern) {
+        return null;
+    }
+
+    @Override
+    public UserPrincipalLookupService getUserPrincipalLookupService() {
+        return null;
+    }
+
+    @Override
+    public WatchService newWatchService() throws IOException {
+        return null;
+    }
+
+    public void addFile(URI uri, byte[] content) {
+        fileContents.put(uri, ByteBuffer.wrap(content));
+    }
+
+    static class CustomMemorySeekableByteChannel implements SeekableByteChannel {
+
+        private final ByteBuffer buffer;
+
+        CustomMemorySeekableByteChannel(ByteBuffer buffer) {
+            this.buffer = buffer;
+        }
+
+        @Override
+        public int read(ByteBuffer dst) throws IOException {
+            int remaining = buffer.remaining();
+            int count = Math.min(remaining, dst.remaining());
+            if (count > 0) {
+                ByteBuffer slice = buffer.slice();
+                slice.limit(count);
+                dst.put(slice);
+                buffer.position(buffer.position() + count);
+            }
+            return count;
+        }
+
+        @Override
+        public int write(ByteBuffer src) throws IOException {
+            int count = src.remaining();
+            buffer.put(src);
+            return count;
+        }
+
+        @Override
+        public long position() throws IOException {
+            return buffer.position();
+        }
+
+        @Override
+        public SeekableByteChannel position(long newPosition) throws IOException {
+            buffer.position((int) newPosition);
+            return this;
+        }
+
+        @Override
+        public long size() throws IOException {
+            return buffer.limit();
+        }
+
+        @Override
+        public SeekableByteChannel truncate(long size) throws IOException {
+            buffer.limit((int) size);
+            return this;
+        }
+
+        @Override
+        public boolean isOpen() {
+            return true; // Always open
+        }
+
+        @Override
+        public void close() throws IOException {
+            // No resources to close
+        }
+    }
+
+}
diff --git a/core/processor/src/test/java/io/quarkus/annotation/processor/fs/CustomMemoryFileSystemProvider.java b/core/processor/src/test/java/io/quarkus/annotation/processor/fs/CustomMemoryFileSystemProvider.java
new file mode 100644
index 0000000000000..8d28a7ae672a6
--- /dev/null
+++ b/core/processor/src/test/java/io/quarkus/annotation/processor/fs/CustomMemoryFileSystemProvider.java
@@ -0,0 +1,152 @@
+package io.quarkus.annotation.processor.fs;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URI;
+import java.nio.ByteBuffer;
+import java.nio.channels.SeekableByteChannel;
+import java.nio.file.AccessMode;
+import java.nio.file.CopyOption;
+import java.nio.file.DirectoryStream;
+import java.nio.file.FileStore;
+import java.nio.file.FileSystem;
+import java.nio.file.LinkOption;
+import java.nio.file.NoSuchFileException;
+import java.nio.file.OpenOption;
+import java.nio.file.Path;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.attribute.FileAttribute;
+import java.nio.file.spi.FileSystemProvider;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Set;
+
+public class CustomMemoryFileSystemProvider extends FileSystemProvider {
+
+    private static final String MEM = "mem";
+
+    private static Map<URI, ByteBuffer> fileContents = new HashMap();
+
+    public static void reset() {
+        fileContents = new HashMap();
+    }
+
+    public static Set<URI> getCreatedFiles() {
+        return fileContents.keySet();
+    }
+
+    @Override
+    public String getScheme() {
+        return MEM;
+    }
+
+    @Override
+    public FileSystem newFileSystem(URI uri, Map<String, ?> env) throws IOException {
+        // There's a bit of a disconnect here between the Elementary JavaFileManager and the memory filesystem,
+        // even though both are in-memory filesystems
+        return new CustomMemoryFileSystem(this);
+    }
+
+    @Override
+    public FileSystem getFileSystem(URI uri) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public Path getPath(URI uri) {
+
+        if (uri.getScheme() == null || !uri.getScheme()
+                .equalsIgnoreCase(MEM)) {
+            throw new IllegalArgumentException("For URI " + uri + ", URI scheme is not '" + MEM + "'");
+
+        }
+
+        // TODO what should we do here? Can we use the java file manager used by Elementary?
+        try {
+            return Path.of(File.createTempFile("mem-fs", "adhoc")
+                    .toURI());
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    @Override
+    public SeekableByteChannel newByteChannel(Path path, Set<? extends OpenOption> options, FileAttribute<?>... attrs)
+            throws IOException {
+        if (fileContents.containsKey(path.toUri())) {
+            ByteBuffer buffer = fileContents.get(path.toUri());
+            return new CustomMemoryFileSystem.CustomMemorySeekableByteChannel(buffer);
+        } else {
+            throw new NoSuchFileException(path.toString());
+        }
+    }
+
+    @Override
+    public DirectoryStream<Path> newDirectoryStream(Path dir, DirectoryStream.Filter<? super Path> filter) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void createDirectory(Path dir, FileAttribute<?>... attrs) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void delete(Path path) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void copy(Path source, Path target, CopyOption... options) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void move(Path source, Path target, CopyOption... options) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public boolean isSameFile(Path path1, Path path2) throws IOException {
+        return path1.equals(path2);
+    }
+
+    @Override
+    public boolean isHidden(Path path) throws IOException {
+        return false;
+    }
+
+    @Override
+    public FileStore getFileStore(Path path) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void checkAccess(Path path, AccessMode... modes) throws IOException {
+        if (!fileContents.containsKey(path.toUri())) {
+            throw new NoSuchFileException(path.toString());
+        }
+    }
+
+    @Override
+    public <V extends java.nio.file.attribute.FileAttributeView> V getFileAttributeView(Path path, Class<V> type,
+            LinkOption... options) {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public <A extends BasicFileAttributes> A readAttributes(Path path, Class<A> type, LinkOption... options)
+            throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public Map<String, Object> readAttributes(Path path, String attributes, LinkOption... options) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+
+    @Override
+    public void setAttribute(Path path, String attribute, Object value, LinkOption... options) throws IOException {
+        throw new UnsupportedOperationException();
+    }
+}
diff --git a/core/processor/src/test/resources/META-INF/services/java.nio.file.spi.FileSystemProvider b/core/processor/src/test/resources/META-INF/services/java.nio.file.spi.FileSystemProvider
new file mode 100644
index 0000000000000..9582882517a77
--- /dev/null
+++ b/core/processor/src/test/resources/META-INF/services/java.nio.file.spi.FileSystemProvider
@@ -0,0 +1 @@
+io.quarkus.annotation.processor.fs.CustomMemoryFileSystemProvider
\ No newline at end of file
diff --git a/core/processor/src/test/resources/io/quarkus/deployment/annotations/BuildStep.java b/core/processor/src/test/resources/io/quarkus/deployment/annotations/BuildStep.java
new file mode 100644
index 0000000000000..944813a9d720a
--- /dev/null
+++ b/core/processor/src/test/resources/io/quarkus/deployment/annotations/BuildStep.java
@@ -0,0 +1,13 @@
+package io.quarkus.deployment.annotations;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.METHOD)
+public @interface BuildStep {
+    // FAKE! FAKE! This is only here so we can test without introducing a circular dependency
+
+}
\ No newline at end of file
diff --git a/core/processor/src/test/resources/org/acme/examples/ArbitraryBuildItem.java b/core/processor/src/test/resources/org/acme/examples/ArbitraryBuildItem.java
new file mode 100644
index 0000000000000..ecb7fb4ee6ee6
--- /dev/null
+++ b/core/processor/src/test/resources/org/acme/examples/ArbitraryBuildItem.java
@@ -0,0 +1,6 @@
+package org.acme.examples;
+
+import io.quarkus.builder.item.MultiBuildItem;
+
+public final class ArbitraryBuildItem extends MultiBuildItem {
+}
\ No newline at end of file
diff --git a/core/processor/src/test/resources/org/acme/examples/ClassWithBuildStep.java b/core/processor/src/test/resources/org/acme/examples/ClassWithBuildStep.java
new file mode 100644
index 0000000000000..8dbecc4bff2bc
--- /dev/null
+++ b/core/processor/src/test/resources/org/acme/examples/ClassWithBuildStep.java
@@ -0,0 +1,10 @@
+package org.acme.examples;
+
+import io.quarkus.deployment.annotations.BuildStep;
+
+public class ClassWithBuildStep {
+    @BuildStep
+    ArbitraryBuildItem feature() {
+        return new ArbitraryBuildItem();
+    }
+}
diff --git a/core/processor/src/test/resources/org/acme/examples/ClassWithoutBuildStep.java b/core/processor/src/test/resources/org/acme/examples/ClassWithoutBuildStep.java
new file mode 100644
index 0000000000000..b40b6d25d2059
--- /dev/null
+++ b/core/processor/src/test/resources/org/acme/examples/ClassWithoutBuildStep.java
@@ -0,0 +1,6 @@
+package org.acme.examples;
+
+public class ClassWithoutBuildStep {
+
+
+}