1 file changed, 19 insertions, 0 deletions
diff --git a/tests/extensions/harness.lua b/tests/extensions/harness.lua
index 1e2fe08..78e491e 100644
--- a/tests/extensions/harness.lua
+++ b/tests/extensions/harness.lua
@@ -160,6 +160,25 @@ function harness.redirect_file(from, to)
 	path_map[from] = to
 end
 
+-- Set or clear an environment variable as a script sees it, for a check
+-- that needs the environment to differ from the one the shell gave this
+-- run. A variable set to nil reads as unset.
+local env_map = nil
+
+function harness.setenv(name, value)
+	if env_map == nil then
+		env_map = {}
+		local real_getenv = os.getenv
+		os.getenv = function(key)
+			if env_map[key] == nil then
+				return real_getenv(key)
+			end
+			return env_map[key] or nil
+		end
+	end
+	env_map[name] = value or false
+end
+
 -- Deterministic bytes standing in for a digest, built from djb2 style lanes
 -- in plain arithmetic so they compute the same on every Lua version. Not
 -- cryptographic, just stable and collision-shy enough for the checks.