diff --git a/games/devtest/mods/unittests/init.lua b/games/devtest/mods/unittests/init.lua
index 724334326..a971632c9 100644
--- a/games/devtest/mods/unittests/init.lua
+++ b/games/devtest/mods/unittests/init.lua
@@ -12,6 +12,7 @@ unittests.list = {}
 --   player = false, -- Does test require a player?
 --   map = false, -- Does test require map access?
 --   async = false, -- Does the test run asynchronously? (read notes above!)
+--   random = false, -- Does the test use math.random directly or indirectly?
 -- }
 function unittests.register(name, func, opts)
 	local def = table.copy(opts or {})
@@ -47,8 +48,18 @@ local function await(invoke)
 	return coroutine.yield()
 end
 
+local function printf(fmt, ...)
+	print(fmt:format(...))
+end
+
 function unittests.run_one(idx, counters, out_callback, player, pos)
 	local def = unittests.list[idx]
+	local seed
+	if def.random then
+		seed = core.get_us_time()
+		math.randomseed(seed)
+	end
+
 	if not def.player then
 		player = nil
 	elseif player == nil then
@@ -70,8 +81,10 @@ function unittests.run_one(idx, counters, out_callback, player, pos)
 		if not status then
 			core.log("error", err)
 		end
-		print(string.format("[%s] %s - %dms",
-			status and "PASS" or "FAIL", def.name, ms_taken))
+		printf("[%s] %s - %dms", status and "PASS" or "FAIL", def.name, ms_taken)
+		if seed and not status then
+			printf("Random was seeded to %d", seed)
+		end
 		counters.time = counters.time + ms_taken
 		counters.total = counters.total + 1
 		if status then
@@ -160,11 +173,11 @@ function unittests.run_all()
 	-- Print stats
 	assert(#unittests.list == counters.total)
 	print(string.rep("+", 80))
-	print(string.format("Devtest Unit Test Results: %s",
-	counters.total == counters.passed and "PASSED" or "FAILED"))
-	print(string.format("    %d / %d failed tests.",
-	counters.total - counters.passed, counters.total))
-	print(string.format("    Testing took %dms total.", counters.time))
+	local passed = counters.total == counters.passed
+	printf("Devtest Unit Test Results: %s", passed and "PASSED" or "FAILED")
+	printf("    %d / %d failed tests.",
+		counters.total - counters.passed, counters.total)
+	printf("    Testing took %dms total.", counters.time)
 	print(string.rep("+", 80))
 	unittests.on_finished(counters.total == counters.passed)
 	return counters.total == counters.passed
diff --git a/games/devtest/mods/unittests/raycast.lua b/games/devtest/mods/unittests/raycast.lua
index db5e78b34..1dc196cc5 100644
--- a/games/devtest/mods/unittests/raycast.lua
+++ b/games/devtest/mods/unittests/raycast.lua
@@ -36,6 +36,28 @@ end
 unittests.register("test_raycast_pointabilities", test_raycast_pointabilities, {map=true})
 
 local function test_raycast_noskip(_, pos)
+	local function random_point_in_area(min, max)
+		local extents = max - min
+		local v = extents:multiply(vector.new(
+			math.random(),
+			math.random(),
+			math.random()
+		))
+		return min + v
+	end
+
+	-- FIXME a variation of this unit test fails in an edge case.
+	-- This is because Luanti does not handle perfectly diagonal raycasts correctly:
+	-- Perfect diagonals collide with neither "outside" face and may thus "pierce" nodes.
+	-- Enable the following code to reproduce:
+	if 0 == 1 then
+		pos = vector.new(6, 32, -3)
+		math.randomseed(1596190898)
+		function random_point_in_area(min, max)
+			return min:combine(max, math.random)
+		end
+	end
+
 	local function cuboid_minmax(extent)
 		return pos:offset(-extent, -extent, -extent),
 				pos:offset(extent, extent, extent)
@@ -62,10 +84,10 @@ local function test_raycast_noskip(_, pos)
 	for _ = 1, 100 do
 		local ray_start
 		repeat
-			ray_start = vector.random_in_area(cuboid_minmax(r))
+			ray_start = random_point_in_area(cuboid_minmax(r))
 		until not ray_start:in_area(cuboid_minmax(1.501))
 		-- Pick a random position inside the dirt
-		local ray_end = vector.random_in_area(cuboid_minmax(1.499))
+		local ray_end = random_point_in_area(cuboid_minmax(1.499))
 		-- The first pointed thing should have only air "in front" of it,
 		-- or a dirt node got falsely skipped.
 		local pt = core.raycast(ray_start, ray_end, false, false):next()
@@ -78,4 +100,4 @@ local function test_raycast_noskip(_, pos)
 	vm:write_to_map()
 end
 
-unittests.register("test_raycast_noskip", test_raycast_noskip, {map = true})
+unittests.register("test_raycast_noskip", test_raycast_noskip, {map = true, random = true})