From 1650839e497d3cf7a35a228917aa894913aa9b9b Mon Sep 17 00:00:00 2001
From: Alex Goodman <wagoodman@gmail.com>
Date: Sat, 8 Dec 2018 12:54:58 -0500
Subject: [PATCH] handle scratch images (closes #76)

---
 filetree/efficiency.go      |  7 ++++++-
 filetree/efficiency_test.go | 26 ++++++++++++++++++++++++--
 2 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/filetree/efficiency.go b/filetree/efficiency.go
index b521bff5..68ed320a 100644
--- a/filetree/efficiency.go
+++ b/filetree/efficiency.go
@@ -91,7 +91,12 @@ func Efficiency(trees []*FileTree) (float64, EfficiencySlice) {
 		minimumPathSizes += value.minDiscoveredSize
 		discoveredPathSizes += value.CumulativeSize
 	}
-	score := float64(minimumPathSizes) / float64(discoveredPathSizes)
+	var score float64
+	if discoveredPathSizes == 0 {
+		score = 1.0
+	} else {
+		score = float64(minimumPathSizes) / float64(discoveredPathSizes)
+	}
 
 	sort.Sort(inefficientMatches)
 
diff --git a/filetree/efficiency_test.go b/filetree/efficiency_test.go
index 3ec779f0..e4612011 100644
--- a/filetree/efficiency_test.go
+++ b/filetree/efficiency_test.go
@@ -4,7 +4,7 @@ import (
 	"testing"
 )
 
-func TestEfficencyMap(t *testing.T) {
+func TestEfficency(t *testing.T) {
 	trees := make([]*FileTree, 3)
 	for idx := range trees {
 		trees[idx] = NewFileTree()
@@ -32,7 +32,7 @@ func TestEfficencyMap(t *testing.T) {
 		for _, match := range actualMatches {
 			t.Logf("   match: %+v", match)
 		}
-		t.Fatalf("Expected to find %d inefficient path, but found %d", len(expectedMatches), len(actualMatches))
+		t.Fatalf("Expected to find %d inefficient paths, but found %d", len(expectedMatches), len(actualMatches))
 	}
 
 	if expectedMatches[0].Path != actualMatches[0].Path {
@@ -43,3 +43,25 @@ func TestEfficencyMap(t *testing.T) {
 		t.Errorf("Expected cumulative size of %v but go %v", expectedMatches[0].CumulativeSize, actualMatches[0].CumulativeSize)
 	}
 }
+
+func TestEfficency_ScratchImage(t *testing.T) {
+	trees := make([]*FileTree, 3)
+	for idx := range trees {
+		trees[idx] = NewFileTree()
+	}
+
+	trees[0].AddPath("/nothing", FileInfo{Size: 0})
+
+	var expectedScore = 1.0
+	var expectedMatches = EfficiencySlice{}
+	actualScore, actualMatches := Efficiency(trees)
+
+	if expectedScore != actualScore {
+		t.Errorf("Expected score of %v but go %v", expectedScore, actualScore)
+	}
+
+	if len(actualMatches) > 0 {
+		t.Fatalf("Expected to find %d inefficient paths, but found %d", len(expectedMatches), len(actualMatches))
+	}
+
+}