test: Add SpecFixtures helper to derive multiple specs from one fixture

Author: thced

src/test/java/com/retailsvc/http/support/SpecFixtures.java

@@ -0,0 +1,82 @@
+package com.retailsvc.http.support;
+
+import com.google.gson.Gson;
+import com.retailsvc.http.spec.Spec;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.Reader;
+import java.io.UncheckedIOException;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+
+/**
+ * Test-only helper: loads {@code /openapi.json} from the classpath, deep-clones the parsed map, and
+ * re-points {@code servers[0].url} so callers can derive multiple {@link Spec} instances from a
+ * single fixture file.
+ */
+public final class SpecFixtures {
+
+  private SpecFixtures() {}
+
+  /** Loads the test spec and rewrites {@code servers[0].url} to {@code newServerUrl}. */
+  public static Spec specAt(String newServerUrl) {
+    Map<String, Object> raw = readBaseSpec();
+    @SuppressWarnings("unchecked")
+    List<Map<String, Object>> servers = (List<Map<String, Object>>) raw.get("servers");
+    if (servers == null || servers.isEmpty()) {
+      throw new IllegalStateException("test spec has no servers entry");
+    }
+    servers.get(0).put("url", newServerUrl);
+    return Spec.from(raw);
+  }
+
+  private static Map<String, Object> readBaseSpec() {
+    try (InputStream in = SpecFixtures.class.getResourceAsStream("/openapi.json")) {
+      if (in == null) {
+        throw new IllegalStateException("/openapi.json not found on test classpath");
+      }
+      return parse(in);
+    } catch (IOException e) {
+      throw new UncheckedIOException(e);
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  private static Map<String, Object> parse(InputStream in) {
+    Gson gson = new Gson();
+    try (Reader reader = new InputStreamReader(in, StandardCharsets.UTF_8)) {
+      Map<String, Object> root = gson.fromJson(reader, Map.class);
+      return deepClone(root);
+    } catch (IOException e) {
+      throw new UncheckedIOException(e);
+    }
+  }
+
+  @SuppressWarnings("unchecked")
+  private static Map<String, Object> deepClone(Map<String, Object> in) {
+    Map<String, Object> out = new LinkedHashMap<>(in.size());
+    for (var e : in.entrySet()) {
+      out.put(e.getKey(), cloneValue(e.getValue()));
+    }
+    return out;
+  }
+
+  @SuppressWarnings("unchecked")
+  private static Object cloneValue(Object v) {
+    if (v instanceof Map<?, ?> m) {
+      return deepClone((Map<String, Object>) m);
+    }
+    if (v instanceof List<?> l) {
+      List<Object> out = new ArrayList<>(l.size());
+      for (Object item : l) {
+        out.add(cloneValue(item));
+      }
+      return out;
+    }
+    return v;
+  }
+}