Finding class by class id instead of fq name in rename tests.

core/descriptors/src/org/jetbrains/kotlin/name/ClassId.java

@@ -108,4 +108,15 @@ public final class ClassId {
         if (packageFqName.isRoot()) return "/" + relativeClassName;
         return packageFqName.toString().replace('.', '/') + "/" + relativeClassName;
     }
+
+    @NotNull
+    public static ClassId fromString(@NotNull String string) {
+        int lastSlash = string.lastIndexOf("/");
+        if (lastSlash == -1) {
+            throw new IllegalArgumentException("Class id should contain slash: " + string);
+        }
+        FqNameUnsafe relativeClassName = new FqNameUnsafe(string.substring(lastSlash + 1));
+        FqName packageFqName = new FqName(string.substring(0, lastSlash).replace('/', '.'));
+        return new ClassId(packageFqName, relativeClassName, false);
+    }
 }