Add basic tests for DiffSect function

Gopkg.lock

@@ -16,6 +16,12 @@
   packages = ["."]
   revision = "2efee857e7cfd4f3d0138cc3cbb1b4966962b93a"
 
+[[projects]]
+  name = "github.com/davecgh/go-spew"
+  packages = ["spew"]
+  revision = "346938d642f2ec3594ed81d874461961cd0faa76"
+  version = "v1.1.0"
+
 [[projects]]
   branch = "master"
   name = "github.com/mailru/easyjson"
@@ -27,6 +33,18 @@
   ]
   revision = "3fdea8d05856a0c8df22ed4bc71b3219245e4485"
 
+[[projects]]
+  name = "github.com/pmezard/go-difflib"
+  packages = ["difflib"]
+  revision = "792786c7400a136282c1664665ae0a8db921c6c2"
+  version = "v1.0.0"
+
+[[projects]]
+  name = "github.com/stretchr/testify"
+  packages = ["assert"]
+  revision = "f35b8ab0b5a2cef36673838d662e249dd9c94686"
+  version = "v1.2.2"
+
 [[projects]]
   name = "gopkg.in/alecthomas/kingpin.v2"
   packages = ["."]
@@ -36,6 +54,6 @@
 [solve-meta]
   analyzer-name = "dep"
   analyzer-version = 1
-  inputs-digest = "8fa3c7995d44f44fb50c3ab09af2f4488a73b4d1824dfe7839a556fe21612a2b"
+  inputs-digest = "8073c00a23b0d2ae4957e488d26c76aa22aa6351c4e2b005051d532ecd8c9d66"
   solver-name = "gps-cdcl"
   solver-version = 1