Add tests for find_hardlinks

spec/unit/git_cache_spec.rb

@@ -106,7 +106,35 @@ module Omnibus
     end
 
     describe "#find_hardlinks" do
-      pending
+      let(:regular_file_stat) do
+        stat = double(File::Stat)
+        allow(stat).to receive(:ftype).and_return(:file)
+        allow(stat).to receive(:nlink).and_return(1)
+        stat
+      end
+
+      let(:hardlinked_file_stat) do
+        stat = double(File::Stat)
+        allow(stat).to receive(:ftype).and_return(:file)
+        allow(stat).to receive(:nlink).and_return(2)
+        allow(stat).to receive(:dev).and_return(5)
+        allow(stat).to receive(:ino).and_return(25)
+        stat
+      end
+
+      before do
+        allow(File).to receive(:stat).and_return(regular_file_stat)
+        allow(File).to receive(:stat).with("foo").and_return(hardlinked_file_stat)
+        allow(File).to receive(:stat).with("bar").and_return(hardlinked_file_stat)
+
+        allow(Omnibus::FileSyncer).to receive(:all_files_under).and_return(
+          %w{ foo bar baz quux }
+        )
+      end
+
+      it "returns some hardlinks" do
+        expect(ipc.find_hardlinks).to eq({ "foo" => ["bar"] })
+      end
     end
 
     describe "#restore_hardlinks" do