Improved output on discovery and failures

* Avoids trace when tests fail and include clean error message
* Improved how test are displayed when doing `pytest --only-collect`

Author: ssbarnea

pytest_molecule.py

@@ -38,7 +38,10 @@ def pytest_collect_file(parent, path):
 
 class MoleculeFile(pytest.File):
     def collect(self):
-        yield MoleculeItem("", self)
+        yield MoleculeItem('test', self)
+
+    def __str__(self):
+        return str(self.fspath.relto(os.getcwd()))
 
 
 class MoleculeItem(pytest.Item):
@@ -50,21 +53,36 @@ def runtest(self):
         cwd = os.path.abspath(os.path.join(self.fspath.dirname, '../..'))
         scenario = folders[-1]
         role = folders[-3]  # noqa
-
-        cmd = ['python', '-m', 'molecule', 'test', '-s', scenario]
+        cmd = [sys.executable, '-m', 'molecule', self.name, '-s', scenario]
         print("running: %s (from %s)" % (" " .join(cmd), cwd))
-        # Workaround for STDOUT/STDERR line ordering issue:
-        # https://github.com/pytest-dev/pytest/issues/5449
-        p = subprocess.Popen(
-            cmd,
-            cwd=cwd,
-            stdout=subprocess.PIPE,
-            stderr=subprocess.STDOUT,
-            universal_newlines=True)
-        for line in p.stdout:
-            print(line, end="")
-        p.wait()
-        assert p.returncode == 0
+
+        try:
+            # Workaround for STDOUT/STDERR line ordering issue:
+            # https://github.com/pytest-dev/pytest/issues/5449
+            p = subprocess.Popen(
+                cmd,
+                cwd=cwd,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.STDOUT,
+                universal_newlines=True)
+            for line in p.stdout:
+                print(line, end="")
+            p.wait()
+            if p.returncode != 0:
+                pytest.fail(
+                    "Error code %s returned by: %s" % (
+                        p.returncode, " ".join(cmd)),
+                    pytrace=False)
+        except Exception as e:
+            pytest.fail(
+                "Exception %s returned by: %s" % (e, " ".join(cmd)),
+                pytrace=False)
+
+    def reportinfo(self):
+        return self.fspath, 0, "usecase: %s" % self.name
+
+    def __str__(self):
+        return self.name
 
 
 class MoleculeException(Exception):