Add a functional test.

Author: hjoliver

tests/functional/cylc-set/10-bad-pre.t

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+# THIS FILE IS PART OF THE CYLC WORKFLOW ENGINE.
+# Copyright (C) NIWA & British Crown (Met Office) & Contributors.
+# 
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#-------------------------------------------------------------------------------
+
+# Check that attempting to set an invalid prerequisite doesn't prevent the target
+# task from spawning later on - https://github.com/cylc/cylc-flow/pull/6691
+
+. "$(dirname "$0")/test_header"
+set_test_number 2
+
+install_and_validate
+reftest_run
+
+purge

tests/functional/cylc-set/10-bad-pre/flow.cylc

@@ -0,0 +1,23 @@
+[scheduler]
+    [[events]]
+        inactivity timeout = PT1M
+        abort on inactivity timeout = True
+        stall timeout = PT0S
+        abort on stall timeout = True
+
+[scheduling]
+    [[graph]]
+    R1 = "foo => bar => baz"
+[runtime]
+  [[foo]]
+    script = """
+      # set an invalid prerequisite...
+      cylc set --pre=1/foo ${CYLC_WORKFLOW_ID}//1/baz
+      cylc__job__poll_grep_workflow_log '1/baz does not depend on "1/foo:succeeded"'
+
+      # ...it should not stop us from successfully setting a valid one
+      cylc set --pre=1/bar ${CYLC_WORKFLOW_ID}//1/baz
+      cylc__job__poll_grep_workflow_log -E '1/baz.* => succeeded'
+    """
+  [[bar]]
+  [[baz]]

tests/functional/cylc-set/10-bad-pre/reference.log

@@ -0,0 +1,3 @@
+1/foo -triggered off [] in flow 1
+1/baz -triggered off ['1/bar'] in flow 1
+1/bar -triggered off ['1/foo'] in flow 1