Backport of Add documentation for JUnit output from 'terraform test' …

…into v1.11 (#36388)

* backport of commit 00eb798

* backport of commit e685e91

* backport of commit d8a2323

* backport of commit 97789c6

* backport of commit 1cb62b5

* backport of commit 5510c11

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Co-authored-by: Sarah French <sarah.french@hashicorp.com>
Co-authored-by: Sarah French <15078782+SarahFrench@users.noreply.github.com>

website/docs/cli/commands/test.mdx

@@ -32,6 +32,8 @@ The following options apply to the Terraform `terraform test` command:
 
 * `-json` - Displays machine-readable JSON output for your testing results.
 
+* `-junit-xml=<output file path>` - Saves a test report in JUnit XML format to the specified file. This is currently incompatible with remote test execution using the the `-cloud-run` option. The file path must be relative or absolute.
+
 * `-test-directory=<relative directory>` - Overrides the directory that Terraform looks into for test files. Note that Terraform always loads testing files within the main configuration directory. The default testing directory is `tests`.
 
 * `-verbose` - Prints out the plan or state for each `run` block within a test file, based on the `command` attribute of each `run` block.
@@ -134,3 +136,92 @@ The testing directory must be beneath the main configuration directory, but it c
 > Note: Test files within the root configuration directory are always loaded, regardless of the `-test-directory` value.
 
 We do not recommend changing the default test directory. The option for customization is included for configuration authors who may have included a `tests` submodule in their configuration before the `terraform test` command was released. In general, the default test directory of `tests` should always be used.
+
+
+## Example: Test Output Format Options
+
+Below is a contrived example of Terraform testing that makes assertions about the values of local variables `true` and `false`.
+There are two test files: one contains a passing test, and one contains a failing test.
+
+```hcl
+# main.tf
+locals {
+  true  = "true"
+  false = "true" # incorrect, should be "false"!
+}
+```
+
+The assertion that `local.true == "true"` in `example_1.tftest.hcl` will pass:
+
+```hcl
+# example_1.tftest.hcl
+run "true_is_true" {
+  assert {
+    condition     = local.true == "true"
+    error_message = "local.true did not match expected value"
+  }
+}
+```
+
+The assertion that `local.false == "false"` in `example_2.tftest.hcl` will fail:
+
+```hcl
+# example_2.tftest.hcl
+run "false_is_false" {
+  assert {
+    condition     = local.false == "false"
+    error_message = "local.false did not match expected value"
+  }
+}
+```
+
+### Test output in JUnit XML format, saved to file
+
+Below is the output of the `terraform test -junit-xml=./output.xml` command using the example files above.
+The test output is:
+
+* Printed to the terminal in the default, human-readable format.
+* Also saved in JUnit XML format in the file specified by the flag.
+
+Below is the contents of the resulting `output.xml` file:
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?><testsuites>
+  <testsuite name="example_1.tftest.hcl" tests="1" skipped="0" failures="0" errors="0">
+    <testcase name="true_is_true" classname="example_1.tftest.hcl" time="0.002295" timestamp="2025-01-13T19:23:16Z"></testcase>
+  </testsuite>
+  <testsuite name="example_2.tftest.hcl" tests="1" skipped="0" failures="1" errors="0">
+    <testcase name="false_is_false" classname="example_2.tftest.hcl" time="0.001468" timestamp="2025-01-13T19:23:16Z">
+      <failure message="local.false did not match expected value"><![CDATA[
+Error: Test assertion failed
+
+  on example_2.tftest.hcl line 3, in run "false_is_false":
+   3:     condition     = local.false == "false"
+    ├────────────────
+    │ local.false is "true"
+
+local.false did not match expected value
+]]></failure>
+    </testcase>
+  </testsuite>
+</testsuites>
+```
+
+If a run block contains a failing assertion, the `<testcase>` element will contain a `<failure>` element that includes the error message and further details.
+
+A `<testcase>` element could contain a `<skipped>` element that includes details about why a test was skipped. This could either be due to an error causing remaining run blocks to be skipped, or due to the command being interrupted.
+
+#### Mapping Terraform test command concepts to JUnit XML format
+
+The test report generated when using `-junit-xml` maps Terraform test command concepts to JUnit XML format according to the table below:
+
+| Terraform test concept            | Element in JUnit XML output                 |
+| ----------------------------------| --------------------------------------------|
+| Test directory                    | `<testsuites>`                              |
+| Test file                         | `<testsuite>`                               |
+| Run block                         | `<testcase>`                                |
+| Run block assertion               | None; details are included only on failure  |
+| Test failure                      | `<failure>`                                 |
+| Test was skipped                  | `<skipped>`                                 |
+| Test stopped due to error         | `<error>`                                   |
+| Any unhandled warnings or errors  | `<system-err>`                              |