I was going to submit a pull request, but my branch continually failed to download at around 70%.

 

Basically a fake world that can be used for pre built world scenerios, ai, and the likes of that

 

FakeWorld.class

package net.minecraftforge.common;

import java.io.File;
import java.util.ArrayList;
import java.util.List;
import java.util.logging.Logger;

import cpw.mods.fml.common.FMLCommonHandler;
import cpw.mods.fml.relauncher.Side;
import cpw.mods.fml.relauncher.SideOnly;

import net.minecraft.block.Block;
import net.minecraft.entity.Entity;
import net.minecraft.entity.EnumCreatureType;
import net.minecraft.logging.ILogAgent;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.profiler.Profiler;
import net.minecraft.util.ChunkCoordinates;
import net.minecraft.util.IProgressUpdate;
import net.minecraft.village.VillageCollection;
import net.minecraft.world.ChunkPosition;
import net.minecraft.world.EnumGameType;
import net.minecraft.world.MinecraftException;
import net.minecraft.world.World;
import net.minecraft.world.WorldProvider;
import net.minecraft.world.WorldSettings;
import net.minecraft.world.WorldType;
import net.minecraft.world.chunk.Chunk;
import net.minecraft.world.chunk.IChunkProvider;
import net.minecraft.world.chunk.storage.IChunkLoader;
import net.minecraft.world.storage.IPlayerFileData;
import net.minecraft.world.storage.ISaveHandler;
import net.minecraft.world.storage.WorldInfo;


/**Built to synthesize a running world for usage in test AI, external rendering, 
* and other scenarios which may occur before a loaded world is available, or where
* utilization of a running world is undesirable*/
public class FakeWorld extends World{
private int[][][] idArray;
private int[][][] metaArray;
private int factor = 3;
private boolean replace = false;
private final List<Entity> spawnOrder = new ArrayList(5);

private static final Profiler dummyProfiler = new Profiler();
private static final ILogAgent dummyLogger = new dudLog();

public FakeWorld(EnumGameType type) {
	super(new dudSave(), "pseudo", new dudProvider(), new WorldSettings(0, type, false, false, WorldType.DEFAULT), dummyProfiler, dummyLogger);
	this.setBlockArray(this.getDefaultIdArray());
	this.chunkProvider = new dudCP(this);
	this.villageCollectionObj = new VillageCollection(this);
	this.provider.registerWorld(this);
	this.chunkProvider = this.createChunkProvider();
	this.calculateInitialSkylight();
	this.provider.calculateInitialWeather();
}

private static final class dudProvider extends WorldProvider{
	@Override
	public String getDimensionName() {
		return "pseudo";
	}
}

private static final class dudSave implements ISaveHandler{

	@Override
	public WorldInfo loadWorldInfo() {return null;}

	@Override
	public void checkSessionLock() throws MinecraftException {}

	@Override
	public IChunkLoader getChunkLoader(WorldProvider worldprovider) {return null;}

	@Override
	public void saveWorldInfoWithPlayer(WorldInfo worldinfo, NBTTagCompound nbttagcompound) {}

	@Override
	public void saveWorldInfo(WorldInfo worldinfo) {}

	@Override
	public IPlayerFileData getSaveHandler(){return null;}

	@Override
	public void flush() {}

	@Override
	public File getMapFileFromName(String s) {return null;}

	@Override
	public String getWorldDirectoryName() {
		return "";
	}
}

private static final class dudLog implements ILogAgent{

	@Override
	public void logInfo(String s) {


	}

	@Override
	@SideOnly(Side.SERVER)
	public Logger getServerLogger() {

		return FMLCommonHandler.instance().getFMLLogger();
	}

	@Override
	public void logWarning(String s) {


	}

	@Override
	public void logWarningFormatted(String s, Object... var2) {


	}

	@Override
	public void logWarningException(String s, Throwable throwable) {


	}

	@Override
	public void logSevere(String s) {


	}

	@Override
	public void logSevereException(String s, Throwable throwable) {			
	}

	@Override
	@SideOnly(Side.CLIENT)
	public void logFine(String s) {			
	}

}

private static final class dudCP implements IChunkProvider{

	private final FakeWorld theWorld;

	public dudCP(FakeWorld w){theWorld = w;}

	@Override
	public boolean chunkExists(int i, int j) {
		return true;
	}

	@Override
	public Chunk provideChunk(int i, int j) {
		return new Chunk(theWorld,0,0);
	}

	@Override
	public Chunk loadChunk(int i, int j) {
		return new Chunk(theWorld, 0, 0);
	}

	@Override
	public void populate(IChunkProvider ichunkprovider, int i, int j) {}

	@Override
	public boolean saveChunks(boolean flag, IProgressUpdate iprogressupdate) {
		return false;
	}

	@Override
	public boolean unloadQueuedChunks() {
		return true;
	}

	@Override
	public boolean canSave() {
		return false;
	}

	@Override
	public String makeString() {
		return "fake world";
	}

	@Override
	public List getPossibleCreatures(EnumCreatureType enumcreaturetype,
			int i, int j, int k) {
		return null;
	}

	@Override
	public ChunkPosition findClosestStructure(World world, String s, int i,
			int j, int k) {
		return new ChunkPosition(0,0,0);
	}

	@Override
	public int getLoadedChunkCount() {
		return 1;
	}

	@Override
	public void recreateStructures(int i, int j) {}

	@Override
	public void func_104112_b() {}

}

//Fake World specific usage features

/**returns the default array of a layer of air above a layer of grass
 * above a layer of dirt*/
public int[] getDefaultIdArray(){
	int[] r = new int[27];
	for(int i = 0; i < r.length; i++)
		if(i < 18)
			r[i] = 0;
		else if( i < 9)
			r[i] = Block.grass.blockID;
		else
			r[i] = Block.dirt.blockID;
	return r;
}

/**Builds layers (x & z) of the given int values. Can be used for block and meta array building*/
public int[] buildHorizontalLayers(int...i){
	int[] builder = new int[(int) Math.pow(i.length, 3)];
	int a = -1;
	for(int y: i)
		for(int z = 0; z < i.length; z++)
			for(int x = 0; x < i.length; x++)
				builder[a++] = i[y];
	return builder;
}


/**sets whether or not external calls can replace the values in the meta and id arrays*/
public void setCanBlockValuesBeReplaced(boolean b){
	replace = b;
}

/**Sets up a blockID array to return during World.getBlockId && World.getBlockMetadata via
 * Integer arrays. Integer array must be a cubic (^3) factor. the getBlock methods then return
 *  a block/meta depending on relative position read in the array set up in Y,X,Z format. The 
 *  The arrays are checked to make sure the lengths are equivalent, the meta ids are not greater
 *  than 15, the blocks are logical value, and the array is a round cubic factor
 *  @param ids The block ID array
 *  @param metas The block metadata array
 *  */
public void setBlockArrays(int[] ids, int[] metas){
	try{
		if(ids.length != metas.length) 
			throw new Throwable("Id and meta arrays must be equivalent in length");
		for(int i = 0; i < ids.length; i++){
			if(ids[i] < 0 || i >= Block.blocksList.length)
				throw new Throwable("All Id values must be within range of 0 to " + Block.blocksList.length);
			else if(metas[i] > 16 || i < 0)
				throw new Throwable("All meta values must be within the range of 0 to 15");
		}
		double fact = Math.cbrt(ids.length);
		int a = this.factor;
		this.factor = (int)fact;
		if(fact != this.factor)
			if(fact != this.factor || this.factor == 0){ 
				this.factor = a;
				throw new Throwable("Block Return arrays must be a round, cubic this.factor");
			}
		int i = 0;
		this.idArray = new int[this.factor][this.factor][this.factor];
		this.metaArray = new int[this.factor][this.factor][this.factor];
		for(int x = 0; x < this.factor; x++)
			for(int z = 0; z < this.factor; z++)
				for(int y = 0; y < this.factor; y++){
					this.idArray[x]
							[y]
									[z] 
											= ids[i];
					this.metaArray[x][y][z] = metas[i];
					i++;
				}

	}catch(Throwable t){
		t.printStackTrace();
	}
}
/**Sets up a blockID array to return during World.getBlockId && World.getBlockMetadata
 * @param ids blockId array. the meta array will be built as an array of the same length
 * but with all metadata values at 0*/
public void setBlockArray(int[] ids){
	int[] metas = new int[ids.length];
	for(int i = 0; i < ids.length; i++)
		metas[0] = 0;
	this.setBlockArrays(ids, metas);
}
/**Empties the spawn order list*/
public void flushSpawnRetention(){
	spawnOrder.clear();
}
/**Retrieves the entity spawn order list, empties it*/
public List<Entity> getSpawnOrder(){
	List l = spawnOrder;
	this.flushSpawnRetention();
	return l;
}
/**Gets the latest spawned entity, Removes from spawn order, Be sure to catch null returns*/
public Entity getLastSpawned(){
	Entity e = null;
	if(!spawnOrder.isEmpty()){
		e = spawnOrder.get(0);
		spawnOrder.remove(0);
	}
	return e;
}


/*Begin pseudo world overrides*/

@Override
public void tickBlocksAndAmbiance(){
	for(int x = 0; x < this.factor; x++)
		for(int z = 0; z < this.factor; z++)
			for(int y = 0; y < this.factor; y++)
				Block.blocksList[this.idArray[y][x][z]].updateTick(this, x, y, z, this.rand);
}


@Override
public boolean setBlock(int x, int y, int z, int id){
	if(replace)
		this.idArray[y >= this.factor ? this.factor : y < 0 ? 0 : y][x % this.factor][z % this.factor] = id;
	return replace;
}

@Override
public boolean setBlock(int x, int y, int z, int id, int meta, int flag){
	if(replace){
		this.idArray[y > this.factor ? this.factor : y < 0 ? 0 : y][x % this.factor][z % this.factor] = id;
		this.metaArray[y > this.factor ? this.factor : y < 0 ? 0 : y][x % this.factor][z % this.factor] = meta;
	}
	return replace;
}

@Override
public boolean setBlockMetadataWithNotify(int x, int y, int z, int meta, int flag){
	if(replace)
		this.metaArray[y > this.factor ? this.factor : y < 0 ? 0 : y][x % this.factor][z % this.factor] = meta;
	return replace;
}

@Override
public void tick(){
	this.tickBlocksAndAmbiance();
	this.tickUpdates(true);
	this.updateWeather();
	this.updateEntities();	
}


@Override
public boolean setBlockToAir(int x, int y, int z){
	if(replace)
		this.idArray[y > this.factor ? this.factor : y < 0 ? 0 : y][x % this.factor][z % this.factor] = 0;
	return replace;
}

@Override
public boolean blockExists(int x, int y, int z){
	return getBlockId(x,y,z) != 0;
}

@Override
public int getBlockId(int x, int y, int z){
	return this.idArray[y > this.factor ? this.factor : y < 0 ? 0 : y][x % this.factor][z % this.factor];
}

@Override
public int getBlockMetadata(int x, int y, int z){
	return this.idArray[y > this.factor ? this.factor : y < 0 ? 0 : y][x % this.factor][z % this.factor];
}

@Override
protected IChunkProvider createChunkProvider() {
	return new dudCP(this);
}

@Override
public Entity getEntityByID(int i) {
	for(Entity e : (List<Entity>)this.loadedEntityList)
		if(e.entityId == i)
			return e;
	return null;
}

@Override
public boolean spawnEntityInWorld(Entity e){
	this.spawnOrder.add(e);
	return super.spawnEntityInWorld(e);
}

@Override
public ChunkCoordinates getSpawnPoint(){
	return new ChunkCoordinates(0,0,0);
}

}

FakeWorldFactory.class

package net.minecraftforge.common;

import net.minecraft.world.EnumGameType;

/**Holds a constant fake world*/
public final class FakeWorldFactory {
private static final FakeWorld instance = new FakeWorld(EnumGameType.SURVIVAL);
private static final FakePlayer psuedo = new FakePlayer(instance, "Psuedo");
/**NOTE: Treat this world as a volatile platform. You should always update the Block array
 * as a precaution for array edits done by other mods
 * @return the constant {@link FakeWorld} value*/
public static FakeWorld getDefault(){
	return instance;
}
/**This gives access to a world safe player instance. Safe for various edits and such
 * @return returns a constant {@link FakePlayer} which has a worldObj set to the constant FakeWorld*/
public static FakePlayer getPseudoPlayer(){
	return psuedo;
}
}

Just as a warning:

 

Make sure this plays nice with Mystcraft.  Mystcraft and Secret Rooms had a conflict for a while, because Secret Rooms used a FakeWorld object and there were some things assumed about it (by one mod or the other) that were untrue and caused null pointer exceptions.

 

(I think Mystcraft kept trying to cause lightning in the fakeworld because it was unable to tell that it was fake, but the fakeworld had no lightning functions, but I could be wrong)