Make tests for BuildWithEnvironment clearer

gexec/build_test.go

diff --git a/gexec/build_test.go b/gexec/build_test.go
index a2f1ccd..c090339 100644
--- a/gexec/build_test.go
+++ b/gexec/build_test.go
@@ -40,28 +40,20 @@
 
 var _ = Describe(".BuildWithEnvironment", func() {
 	var err error
+	env := map[string]string{
+		"GOOS":   "linux",
+		"GOARCH": "amd64",
+	}
 
 	It("compiles the specified package with the specified env vars", func() {
-		env := map[string]string{
-			"GOOS":   "linux",
-			"GOARCH": "amd64",
-		}
-
 		compiledPath, err := gexec.BuildWithEnvironment(packagePath, env)
 		Ω(err).ShouldNot(HaveOccurred())
 		Ω(compiledPath).Should(BeAnExistingFile())
 	})
 
 	It("returns the environment to a good state", func() {
-		knownGoodEnv := os.Environ()
-
-		env := map[string]string{
-			"THIS_ENV_VAR": "SHOULD_NOT_BE_SET",
-		}
-
 		_, err = gexec.BuildWithEnvironment(packagePath, env)
 		Ω(err).ShouldNot(HaveOccurred())
-
-		Ω(os.Environ()).Should(Equal(knownGoodEnv))
+		Ω(os.Environ()).ShouldNot(ContainElement("GOOS=linux"))
 	})
 })