From 10f275fb769ce06a02444adb011ed0e269e0948f Mon Sep 17 00:00:00 2001
From: kmoe <5575356+kmoe@users.noreply.github.com>
Date: Wed, 18 May 2022 16:15:45 +0100
Subject: [PATCH] document test env vars

---
 CONTRIBUTING.md | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index a12cf6bd..e6d35496 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -38,6 +38,15 @@ Command options are implemented using the functional variadic options pattern. F
 
 We aim for full test coverage of all Terraform CLI commands implemented in `tfexec`, with as many combinations of command-line options as possible. New command implementations will not be merged without both unit and end-to-end tests.
 
+### Environment variables
+
+The following environment variables can be set during testing:
+
+ - `TFEXEC_E2ETEST_VERSIONS`: When set to a comma-separated list of version strings, this overrides the default list of Terraform versions for end-to-end tests, and runs those tests against only the versions supplied.
+ - `TFEXEC_E2ETEST_TERRAFORM_PATH`: When set to the path of a valid local Terraform executable, only tests appropriate to that executable's version are run. No other versions are downloaded or run. Note that this means that tests using `runTestVersions()` will only run if the test version matches the local executable exactly.
+
+If both of these environment variables are set, `TFEXEC_E2ETEST_TERRAFORM_PATH` takes precedence, and any other versions specified in `TFEXEC_E2ETEST_VERSIONS` are ignored.
+
 ### Unit tests
 
 Unit tests live alongside command implementations in `tfexec/`. A unit test asserts that the *string* version of the `exec.Cmd` returned by the `*Cmd` function (e.g. `refreshCmd`) is as expected. Minimally, commands must be tested with no options passed ("defaults"), and with all options set to non-default values. The `assertCmd()` helper can be used for this purpose. Please see `tfexec/init_test.go` for a reasonable starting point.