diff --git a/testes/lush/builtins.lua b/testes/lush/builtins.lua
index 5a58a4da..72a2ffb5 100644
--- a/testes/lush/builtins.lua
+++ b/testes/lush/builtins.lua
@@ -3,6 +3,8 @@
 
 print "testing shell builtins"
 
+local interp = require("lush.testutil").INTERP
+
 -- === __builtins is NOT in _G (internal, stored in registry) ===
 
 do
@@ -132,7 +134,7 @@ end
 
 -- exec replaces process (test in subprocess)
 do
-  local r = `sh -c './lua -e "os.exit(42)"'`
+  local r = lush.capture("sh -c '" .. interp .. " -e \"os.exit(42)\"'")
   assert(r.code == 42, "subprocess exit code: " .. tostring(r.code))
 end
 
diff --git a/testes/lush/config.lua b/testes/lush/config.lua
index 3e8ca048..41b02bcf 100644
--- a/testes/lush/config.lua
+++ b/testes/lush/config.lua
@@ -3,6 +3,8 @@
 
 print "testing configuration"
 
+local INTERP = require("lush.testutil").INTERP
+
 -- helper: get a unique temp directory
 local tmpbase = os.tmpname()
 os.remove(tmpbase)  -- tmpname creates the file on some systems
@@ -21,10 +23,10 @@ local function rmrf(path)
   os.execute('rm -rf "' .. path .. '"')
 end
 
--- helper: run ./lua -i with XDG_CONFIG_HOME set, feed it a command via stdin
+-- helper: run interpreter -i with XDG_CONFIG_HOME set, feed it a command via stdin
 local function run_with_config(xdg_dir, input)
   local cmd = string.format(
-    'printf "%%s\\n" "%s" | XDG_CONFIG_HOME="%s" ./lua -i 2>&1',
+    'printf "%%s\\n" "%s" | XDG_CONFIG_HOME="%s" ' .. INTERP .. ' -i 2>&1',
     input, xdg_dir)
   local f = io.popen(cmd)
   local output = f:read("*a")
@@ -32,10 +34,10 @@ local function run_with_config(xdg_dir, input)
   return output
 end
 
--- helper: run ./lua -E -i with XDG_CONFIG_HOME set
+-- helper: run interpreter -E -i with XDG_CONFIG_HOME set
 local function run_with_config_E(xdg_dir, input)
   local cmd = string.format(
-    'printf "%%s\\n" "%s" | XDG_CONFIG_HOME="%s" ./lua -E -i 2>&1',
+    'printf "%%s\\n" "%s" | XDG_CONFIG_HOME="%s" ' .. INTERP .. ' -E -i 2>&1',
     input, xdg_dir)
   local f = io.popen(cmd)
   local output = f:read("*a")
diff --git a/testes/lush/globbing.lua b/testes/lush/globbing.lua
index 2191f811..954af613 100644
--- a/testes/lush/globbing.lua
+++ b/testes/lush/globbing.lua
@@ -7,7 +7,7 @@ print "testing globbing and tilde expansion"
 
 -- *.lua should expand to matching files (we know lush test files exist)
 do
-  local r = `echo *.c`
+  local r = `echo ../*.c`
   local out = r.stdout:gsub("\n$", "")
   -- should NOT be the literal "*.c" since .c files exist in the project
   assert(out ~= "*.c", "expected *.c to expand, got literal: " .. out)
@@ -125,7 +125,7 @@ end
 -- === expansion in pipelines ===
 
 do
-  local r = `echo *.c | head -1`
+  local r = `echo ../*.c | head -1`
   local out = r.stdout:gsub("\n$", "")
   -- pipeline should have expanded *.c before piping
   assert(out ~= "*.c", "glob not expanded in pipeline, got: " .. out)
diff --git a/testes/lush/prompt.lua b/testes/lush/prompt.lua
index f793bae1..be0cddbd 100644
--- a/testes/lush/prompt.lua
+++ b/testes/lush/prompt.lua
@@ -3,6 +3,8 @@
 
 print "testing prompt system"
 
+local INTERP = require("lush.testutil").INTERP
+
 -- helper: get a unique temp directory
 local tmpbase = os.tmpname()
 os.remove(tmpbase)  -- tmpname creates the file on some systems
@@ -21,7 +23,7 @@ local function rmrf(path)
   os.execute('rm -rf "' .. path .. '"')
 end
 
--- helper: run ./lua -i with config, use print() to reveal prompt state
+-- helper: run interpreter -i with config, use print() to reveal prompt state
 local function run_lua(input, config_content)
   local tmpdir = tmpbase .. "_run"
   mkdir(tmpdir .. "/lush")
@@ -29,7 +31,7 @@ local function run_lua(input, config_content)
     writefile(tmpdir .. "/lush/config.lua", config_content)
   end
   local cmd = string.format(
-    'printf "%%s\\n" %s | XDG_CONFIG_HOME="%s" ./lua -i 2>&1',
+    'printf "%%s\\n" %s | XDG_CONFIG_HOME="%s" ' .. INTERP .. ' -i 2>&1',
     input, tmpdir)
   local f = io.popen(cmd)
   local output = f:read("*a")
diff --git a/testes/lush/testutil.lua b/testes/lush/testutil.lua
new file mode 100644
index 00000000..ec2838e9
--- /dev/null
+++ b/testes/lush/testutil.lua
@@ -0,0 +1,13 @@
+-- testes/lush/testutil.lua
+-- Shared utilities for lush test files.
+
+local M = {}
+
+-- Derive the interpreter path from the arg table.
+-- Works regardless of CWD (project root or testes/).
+local a = arg or ARG
+local i = 0
+while a[i] do i = i - 1 end
+M.INTERP = a[i + 1]
+
+return M