Various VM tests

These are largely copied across from Cobalt's test suite, with some
minor tweaks. It actually exposed one bug in Cobalt, which is pretty
nice.

One interesting thing from the coroutine tests, is that Lua 5.4 (and
one assumes 5.2/5.3) doesn't allow yielding from within the error
handler of xpcall - I rather thought it might.

This doesn't add any of the PUC Lua tests yet - I got a little
distracted.

Also:
 - Allow skipping "keyword" tests, in the style of busted. This is
   implemented on the Java side for now.
 - Fix a bug with os.date("%I", _) not being 2 characters wide.

src/test/java/dan200/computercraft/core/ComputerTestDelegate.java

@@ -42,6 +42,8 @@ import java.util.*;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.locks.Condition;
 import java.util.concurrent.locks.ReentrantLock;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 import java.util.stream.Stream;
 
 import static dan200.computercraft.api.lua.LuaValues.getType;
@@ -67,6 +69,12 @@ public class ComputerTestDelegate
 
     private static final long TIMEOUT = TimeUnit.SECONDS.toNanos( 10 );
 
+    private static final Set<String> SKIP_KEYWORDS = new HashSet<>(
+        Arrays.asList( System.getProperty( "cc.skip_keywords", "" ).split( "," ) )
+    );
+
+    private static final Pattern KEYWORD = Pattern.compile( ":([a-z_]+)" );
+
     private final ReentrantLock lock = new ReentrantLock();
     private Computer computer;
 
@@ -212,18 +220,23 @@ public class ComputerTestDelegate
 
         void runs( String name, Executable executor )
         {
-            DynamicNodeBuilder child = children.get( name );
-            int id = 0;
-            while( child != null )
-            {
-                id++;
-                String subName = name + "_" + id;
-                child = children.get( subName );
-            }
+            if( this.executor != null ) throw new IllegalStateException( name + " is leaf node" );
+            if( children.containsKey( name ) ) throw new IllegalStateException( "Duplicate key for " + name );
 
             children.put( name, new DynamicNodeBuilder( name, executor ) );
         }
 
+        boolean isActive()
+        {
+            Matcher matcher = KEYWORD.matcher( name );
+            while( matcher.find() )
+            {
+                if( SKIP_KEYWORDS.contains( matcher.group( 1 ) ) ) return false;
+            }
+
+            return true;
+        }
+
         DynamicNode build()
         {
             return executor == null
@@ -233,7 +246,9 @@ public class ComputerTestDelegate
 
         Stream<DynamicNode> buildChildren()
         {
-            return children.values().stream().map( DynamicNodeBuilder::build );
+            return children.values().stream()
+                .filter( DynamicNodeBuilder::isActive )
+                .map( DynamicNodeBuilder::build );
         }
     }