From 2bca261c8f1c7d6ac01ad4d196b0a7f953b2dbc0 Mon Sep 17 00:00:00 2001
From: Tim Smith <tsmith84@proton.me>
Date: Sat, 27 Jun 2026 23:04:41 -0700
Subject: [PATCH] Fix NaN coverage percentage when no resources are collected

Coverage#report! computed the percentage as
`(touched / total.to_f * 100).round(2)`. When a run collects no resources
(total == 0), that is `0 / 0.0` which evaluates to NaN. The human ERB
template hides this, but the value still flows into the report hash and
any programmatic/JSON consumer sees NaN.

Extract the math into a coverage_percentage helper that returns 0.0 when
there are no resources, and unit test it.

Signed-off-by: Tim Smith <tsmith84@proton.me>
---
 lib/chefspec/coverage.rb   | 14 +++++++++++++-
 spec/unit/coverage_spec.rb | 21 +++++++++++++++++++++
 2 files changed, 34 insertions(+), 1 deletion(-)
 create mode 100644 spec/unit/coverage_spec.rb

diff --git a/lib/chefspec/coverage.rb b/lib/chefspec/coverage.rb
index a57b6588..02eb756f 100644
--- a/lib/chefspec/coverage.rb
+++ b/lib/chefspec/coverage.rb
@@ -161,7 +161,7 @@ def report!
       report = {}.tap do |h|
         h[:total]     = @collection.size
         h[:touched]   = @collection.count { |_, resource| resource.touched? }
-        h[:coverage]  = ((h[:touched] / h[:total].to_f) * 100).round(2)
+        h[:coverage]  = coverage_percentage(h[:touched], h[:total])
       end
 
       report[:untouched_resources] = @collection.collect do |_, resource|
@@ -179,6 +179,18 @@ def report!
 
     private
 
+    #
+    # The percentage of covered resources, guarding against a division by zero
+    # when no resources were collected (which would otherwise produce NaN).
+    #
+    # @return [Float]
+    #
+    def coverage_percentage(touched, total)
+      return 0.0 if total == 0
+
+      ((touched / total.to_f) * 100).round(2)
+    end
+
     def find(resource)
       @collection[resource.to_s]
     end
diff --git a/spec/unit/coverage_spec.rb b/spec/unit/coverage_spec.rb
new file mode 100644
index 00000000..e155d2b3
--- /dev/null
+++ b/spec/unit/coverage_spec.rb
@@ -0,0 +1,21 @@
+require "spec_helper"
+
+describe ChefSpec::Coverage do
+  subject(:coverage) { described_class.instance }
+
+  describe "#coverage_percentage" do
+    it "returns 0.0 when there are no resources instead of NaN" do
+      result = coverage.send(:coverage_percentage, 0, 0)
+      expect(result).to eq(0.0)
+      expect(result).not_to be_nan
+    end
+
+    it "calculates the touched percentage" do
+      expect(coverage.send(:coverage_percentage, 3, 4)).to eq(75.0)
+    end
+
+    it "rounds to two decimal places" do
+      expect(coverage.send(:coverage_percentage, 1, 3)).to eq(33.33)
+    end
+  end
+end