Test variables

LTF supports test variables: named values you register in Lua and optionally override from the CLI. Tests read them at runtime with ltf.get_var().

Registering variables

Call ltf.register_vars() at Lua top level (not inside a test body). You can place it anywhere, but it’s usually best to keep variables in one file (for example lib/variables.lua).

local ltf = require("ltf")

ltf.register_vars({
  project = "my-project",
})

You can call ltf.register_vars as much as you need and do it across different files as long as the variables you are registering are unique.

Using variables in a test

local ltf = require("ltf")

ltf.test({
  name = "Example Test",
  body = function()
    local project = ltf.get_var("project")
    ltf.log_info("Project is: " .. project)
  end,
})

Variable forms

LTF variables can be registered in one of these five forms:

1) Constant

Fixed value. Cannot be overridden.

ltf.register_vars({
  device_type = "stm32",
})

Use when the test suite is tied to a specific value.

---

2) Required

Must be provided (typically via CLI). No default.

ltf.register_vars({
  serial_port = {},
})

Use when the value depends on the environment (like /dev/ttyUSB0).

---

3) Default

Optional. Uses default unless overridden.

ltf.register_vars({
  baudrate = { default = "115200" },
})

Use when most runs share a common value, but you occasionally change it.

---

4) Enum

Restricted set. Value must be one of values.

ltf.register_vars({
  log_level = {
    values = { "critical", "debug", "info", "warning", "error" },
  },
})

Use when you only want to allow known modes.

---

5) Enum with default

Restricted set + default. Default must be in values.

ltf.register_vars({
  env = {
    default = "dev",
    values = { "dev", "staging", "prod" },
  },
})

Use when there’s a standard choice, but you still want strict allowed values.

---

Setting variables

Pass variables as name=value pairs, separated by commas:

ltf test --vars serial_port=/dev/ttyUSB0,env=staging,log_level=debug

Shorthand:

ltf test -v serial_port=/dev/ttyUSB0,env=staging

You can also set variables by multiple -v/--vars:

ltf test -v serial_port=/dev/ttyUSB0 -v env=staging

If you need to set variable which contains comma(s), just wrap it in quotes:

ltf test -v enumeration="one,two,three",serial_port=/dev/ttyUSB0

Alternatively, variables can also be set via Test Scenarios.

Validation rules

LTF validates variables before any tests run:

• Constant variables cannot be overridden from the CLI.
• For Enum and Enum with default:
• CLI values must be listed in values
• default (if present) must also be listed in values
• If specified variable was not registered LTF will print warning message but continue executing tests.

If validation fails, LTF exits with an error before executing tests.

Example

See project example.