fix(slack): handle scans that produce no findings (#12229)

Co-authored-by: Juhef <117518034+juheff@users.noreply.github.com>
Co-authored-by: Daniel Barranquero <danielbo2001@gmail.com>

prowler/changelog.d/slack-zero-findings.fixed.md

@@ -0,0 +1 @@
+CLI Slack integration (`--slack`) no longer fails when a scan produces no findings: the pass and fail percentages are guarded against a `findings_count` of 0, which previously raised `ZeroDivisionError` and sent `blocks=None` to Slack instead of the summary

prowler/lib/outputs/slack/slack.py

@@ -110,6 +110,20 @@ class Slack:
             list: list of Slack message blocks.
         """
         try:
+            # A scan can legitimately produce no findings, in which case
+            # `findings_count` is 0 and the percentages below would raise
+            # `ZeroDivisionError`.
+            findings_count = stats["findings_count"]
+            pass_percentage = (
+                round(stats["total_pass"] / findings_count * 100, 2)
+                if findings_count
+                else 0
+            )
+            fail_percentage = (
+                round(stats["total_fail"] / findings_count * 100, 2)
+                if findings_count
+                else 0
+            )
             blocks = [
                 {
                     "type": "section",
@@ -128,7 +142,7 @@ class Slack:
                     "type": "section",
                     "text": {
                         "type": "mrkdwn",
-                        "text": f"\n:white_check_mark: *{stats['total_pass']} Passed findings* ({round(stats['total_pass'] / stats['findings_count'] * 100, 2)}%)\n",
+                        "text": f"\n:white_check_mark: *{stats['total_pass']} Passed findings* ({pass_percentage}%)\n",
                     },
                 },
                 {
@@ -148,7 +162,7 @@ class Slack:
                     "type": "section",
                     "text": {
                         "type": "mrkdwn",
-                        "text": f"\n:x: *{stats['total_fail']} Failed findings* ({round(stats['total_fail'] / stats['findings_count'] * 100, 2)}%)\n ",
+                        "text": f"\n:x: *{stats['total_fail']} Failed findings* ({fail_percentage}%)\n ",
                     },
                 },
                 {

tests/lib/outputs/slack/slack_test.py

@@ -205,6 +205,47 @@ class TestSlackIntegration:
             },
         ]
 
+    def test_create_message_blocks_no_findings(self):
+        """A scan that produced no findings must still build a valid message.
+
+        The pass/fail percentages divide by ``stats["findings_count"]``, which is
+        initialised to 0 in ``prowler/lib/outputs/outputs.py``. With no findings
+        that raises ``ZeroDivisionError``, the handler logs it and returns
+        ``None``, and ``send()`` then passes ``blocks=None`` to
+        ``chat_postMessage``.
+        """
+        aws_provider = set_mocked_aws_provider()
+        slack = Slack(SLACK_TOKEN, SLACK_CHANNEL, aws_provider)
+        args = "--slack"
+        stats = {
+            "total_pass": 0,
+            "total_fail": 0,
+            "total_critical_severity_pass": 0,
+            "total_critical_severity_fail": 0,
+            "total_high_severity_fail": 0,
+            "total_high_severity_pass": 0,
+            "total_medium_severity_fail": 0,
+            "total_medium_severity_pass": 0,
+            "total_low_severity_fail": 0,
+            "total_low_severity_pass": 0,
+            "resources_count": 0,
+            "findings_count": 0,
+        }
+
+        blocks = slack.__create_message_blocks__(
+            f"AWS Account *{AWS_ACCOUNT_NUMBER}*", aws_logo, stats, args
+        )
+
+        assert blocks is not None, (
+            "__create_message_blocks__ returned None, so send() passes "
+            "blocks=None to chat_postMessage"
+        )
+        assert isinstance(blocks, list) and blocks
+        # The percentages must degrade to 0% rather than raising.
+        rendered = str(blocks)
+        assert "0 Passed findings* (0%)" in rendered
+        assert "0 Failed findings* (0%)" in rendered
+
     def test_create_message_blocks_azure(self):
         aws_provider = set_mocked_azure_provider()
         slack = Slack(SLACK_TOKEN, SLACK_CHANNEL, aws_provider)