add core:tests_util module & add base_entities test

dev/tests/base_entities.lua

@@ -0,0 +1,24 @@
+local util = require("core:tests_util")
+
+-- Create world and prepare settings
+util.create_demo_world("core:default")
+app.set_setting("chunks.load-distance", 3)
+app.set_setting("chunks.load-speed", 1)
+
+-- Create player
+local pid = player.create("Xerxes")
+player.set_spawnpoint(pid, 0, 100, 0)
+player.set_pos(pid, 0, 100, 0)
+
+-- Wait for chunk to load
+app.sleep_until(function () return block.get(0, 0, 0) ~= -1 end)
+
+-- Place a falling block
+block.place(0, 2, 0, block.index("base:sand"), 0, pid)
+app.tick()
+
+-- Check if the block is falling
+assert(block.get(0, 100, 0) == 0)
+
+-- Wait for the block to fall
+app.sleep_until(function () return block.get(0, 1, 0) == block.index("base:sand") end, 100)