From ad5b3c835f6de90ee3d31734c6a74d2c40a595bc Mon Sep 17 00:00:00 2001
From: Chad Shaffer <chad.shaffer@mycase.com>
Date: Fri, 4 Nov 2016 12:34:56 -0700
Subject: [PATCH] Allow for empty last_run files for parallel tests that end up
 running no tests

---
 CHANGELOG.md              |  2 ++
 lib/simplecov/last_run.rb |  3 ++-
 spec/last_run_spec.rb     | 45 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 spec/last_run_spec.rb

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 4c6dd574..37318f5c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,8 @@ Unreleased ([changes](https://github.com/colszowka/simplecov/compare/v0.12.0...m
 
 ## Bugfixes
 
+* Fix parallel_tests where one thread ends up running no tests. See [#533](https://github.com/colszowka/simplecov/pull/533) (thanks @cshaffer)
+
 0.12.0 2016-07-02 ([changes](https://github.com/colszowka/simplecov/compare/v0.11.2...v0.12.0))
 =================
 
diff --git a/lib/simplecov/last_run.rb b/lib/simplecov/last_run.rb
index 64b2f948..90c41102 100644
--- a/lib/simplecov/last_run.rb
+++ b/lib/simplecov/last_run.rb
@@ -9,7 +9,8 @@ def last_run_path
 
       def read
         return nil unless File.exist?(last_run_path)
-        JSON.parse(File.read(last_run_path))
+        json = File.read(last_run_path)
+        JSON.parse(json) unless json.strip.empty?
       end
 
       def write(json)
diff --git a/spec/last_run_spec.rb b/spec/last_run_spec.rb
new file mode 100644
index 00000000..30793865
--- /dev/null
+++ b/spec/last_run_spec.rb
@@ -0,0 +1,45 @@
+require "helper"
+
+describe SimpleCov::LastRun do
+  subject { SimpleCov::LastRun }
+
+  it "defines a last_run_path" do
+    expect(subject.last_run_path).to eq(File.join(SimpleCov.coverage_path, ".last_run.json"))
+  end
+
+  it "writes json to its last_run_path" do
+    json = []
+    subject.write(json)
+    expect(File.read(subject.last_run_path).strip).to eq(JSON.pretty_generate(json))
+  end
+
+  context "reading" do
+    context "but the last_run file does not exist" do
+      before { File.delete(subject.last_run_path) if File.exist?(subject.last_run_path) }
+
+      it "returns nil" do
+        expect(subject.read).to be_nil
+      end
+    end
+
+    context "a non empty result" do
+      before { subject.write([]) }
+
+      it "reads json from its last_run_path" do
+        expect(subject.read).to eq(JSON.parse("[]"))
+      end
+    end
+
+    context "an empty result" do
+      before do
+        File.open(subject.last_run_path, "w+") do |f|
+          f.puts ""
+        end
+      end
+
+      it "returns nil" do
+        expect(subject.read).to be_nil
+      end
+    end
+  end
+end if SimpleCov.usable?