Add better assert, remove stdout/err redirect

tests/integration/test_buildrequire_invalid_module.py

@@ -0,0 +1,45 @@
+# -*- coding: utf-8 -*-
+# SPDX-License-Identifier: MIT
+import pytest
+from sh import ErrorReturnCode
+
+
+# expected error message
+CANNOT_FIND_ANY_MODULE_BUILDS = "Cannot find any module builds"  # ...
+
+
+def test_buildrequire_invalid_module(pkg_util, scenario, repo, koji):
+    """
+        Run a build with with an invalid 'build_require' module.
+        I.e.: required module is picked in such a way,
+        that it is not tagged according to the the base module (platform) requirements,
+        see platform's modulemd file and its 'koji_tag_with_modules' attribute
+        (e.g.: platform: el-8.1.0 --> rhel-8.1.0-modules-build).
+
+        Koji resolver is expected to not be able to satisfy this build requirement
+        and hence fail the build.
+
+        Assert that:
+        * the module build hasn't been accepted by MBS:
+          rhpkg utility returns something else than 0
+        * "Cannot find any module build..." found on STDERR
+
+        If assert fails:
+        * cancel all triggered module builds.
+
+        """
+
+    repo.bump()
+
+    try:
+        builds = pkg_util.run("--optional", "rebuild_strategy=all")
+
+        for build in builds:
+            print("Canceling module-build {}...".format(build.id))
+            pkg_util.cancel(build)
+
+        pytest.fail("Invalid 'build_require' was satisfied and module build was accepted by MBS!")
+
+    except ErrorReturnCode as e:
+        # expected outcome: build submission fails
+        assert CANNOT_FIND_ANY_MODULE_BUILDS in e.stderr.decode("utf-8")