tmt: Add TMT_TEST env variable to specify single test to run

e.g. `TMT_TEST=test-21-logically-bound-switch make test-tmt`
will run all the tmt setup code then run test-21-logically-bound-switch.
This is useful when developing a test.

Signed-off-by: Chris Kyrouac <[email protected]>

Author: ckyrouac

xtask/src/xtask.rs

@@ -155,7 +155,7 @@ fn update_generated(sh: &Shell) -> Result<()> {
 }
 
 #[context("test-integration")]
-fn test_tmt(sh: &Shell) -> Result<()> {
+fn all_plan_files(sh: &Shell) -> Result<Vec<(u32, String)>> {
     // We need to split most of our tests into separate plans because tmt doesn't
     // support automatic isolation. (xref)
     let mut all_plan_files =
@@ -186,14 +186,26 @@ fn test_tmt(sh: &Shell) -> Result<()> {
                 Ok(acc)
             })?;
     all_plan_files.sort_by_key(|v| v.0);
-    println!("Discovered plans: {all_plan_files:?}");
+    Ok(all_plan_files)
+}
+
+#[context("test-integration")]
+fn test_tmt(sh: &Shell) -> Result<()> {
+    let tests = match std::env::var("TMT_TEST") {
+        Ok(test) => {
+            vec![(0, test)]
+        }
+        Err(_) => all_plan_files(sh)?,
+    };
+
+    println!("Discovered plans: {tests:?}");
 
     cmd!(sh, "cargo run -p tests-integration run-vm prepare-tmt").run()?;
 
     // pull some small images that are used for LBI installation tests
     cmd!(sh, "podman pull {TEST_IMAGES...}").run()?;
 
-    for (_prio, name) in all_plan_files {
+    for (_prio, name) in tests {
         // cc https://pagure.io/testcloud/pull-request/174
         cmd!(sh, "rm -vf /var/tmp/tmt/testcloud/images/disk.qcow2").run()?;
         let verbose_enabled = std::env::var("TMT_VERBOSE")