Move some implicitly shared testing code for bp2build into testing.go.

Test: go test
Change-Id: I403d703184e517dbffbdccb8007229cad00858c1
diff --git a/bp2build/python_binary_conversion_test.go b/bp2build/python_binary_conversion_test.go
index 2054e06..ed509bf 100644
--- a/bp2build/python_binary_conversion_test.go
+++ b/bp2build/python_binary_conversion_test.go
@@ -128,11 +128,11 @@
 		ctx.RegisterForBazelConversion()
 
 		_, errs := ctx.ParseFileList(dir, toParse)
-		if Errored(t, testCase.description, errs) {
+		if errored(t, testCase.description, errs) {
 			continue
 		}
 		_, errs = ctx.ResolveDependencies(config)
-		if Errored(t, testCase.description, errs) {
+		if errored(t, testCase.description, errs) {
 			continue
 		}