Fix nondeterministic failure caused by parallel tests.

Tests no longer run in parallel. Fix a test case that mocked
a global variable mock but never reset it.

One test overrides the `openFile` function to mock a file system
call with a version that always errors. There were two issues with this:

1. The test case never reset openFile to use os.OpenFile
2. The tests could run in parallel which would result in another test case
   calling the mocked version before it could be reset.

Author: inconshreveable

apply_test.go

@@ -49,8 +49,6 @@ func validateUpdate(path string, err error, t *testing.T) {
 }
 
 func TestApplySimple(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestApplySimple"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -62,8 +60,6 @@ func TestApplySimple(t *testing.T) {
 }
 
 func TestApplyOldSavePath(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestApplyOldSavePath"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -84,8 +80,6 @@ func TestApplyOldSavePath(t *testing.T) {
 }
 
 func TestVerifyChecksum(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestVerifyChecksum"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -98,8 +92,6 @@ func TestVerifyChecksum(t *testing.T) {
 }
 
 func TestVerifyChecksumNegative(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestVerifyChecksumNegative"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -115,8 +107,6 @@ func TestVerifyChecksumNegative(t *testing.T) {
 }
 
 func TestApplyPatch(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestApplyPatch"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -135,8 +125,6 @@ func TestApplyPatch(t *testing.T) {
 }
 
 func TestCorruptPatch(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestCorruptPatch"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -152,8 +140,6 @@ func TestCorruptPatch(t *testing.T) {
 }
 
 func TestVerifyChecksumPatchNegative(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestVerifyChecksumPatchNegative"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -263,9 +249,7 @@ func sign(parsePrivKey func([]byte) (crypto.Signer, error), privatePEM string, s
 }
 
 func TestVerifyECSignature(t *testing.T) {
-	t.Parallel()
-
-	fName := "TestVerifySignature"
+	fName := "TestVerifyECSignature"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
 
@@ -281,9 +265,7 @@ func TestVerifyECSignature(t *testing.T) {
 }
 
 func TestVerifyRSASignature(t *testing.T) {
-	t.Parallel()
-
-	fName := "TestVerifySignature"
+	fName := "TestVerifyRSASignature"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
 
@@ -302,8 +284,6 @@ func TestVerifyRSASignature(t *testing.T) {
 }
 
 func TestVerifyFailBadSignature(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestVerifyFailBadSignature"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -324,8 +304,6 @@ func TestVerifyFailBadSignature(t *testing.T) {
 }
 
 func TestVerifyFailNoSignature(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestVerifySignatureWithPEM"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -352,8 +330,6 @@ VBbP/Ff+05HOqwPC7rJMy1VAJLKg7Cw=
 `
 
 func TestVerifyFailWrongSignature(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestVerifyFailWrongSignature"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -372,8 +348,6 @@ func TestVerifyFailWrongSignature(t *testing.T) {
 }
 
 func TestSignatureButNoPublicKey(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestSignatureButNoPublicKey"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -388,8 +362,6 @@ func TestSignatureButNoPublicKey(t *testing.T) {
 }
 
 func TestPublicKeyButNoSignature(t *testing.T) {
-	t.Parallel()
-
 	fName := "TestPublicKeyButNoSignature"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -405,7 +377,6 @@ func TestPublicKeyButNoSignature(t *testing.T) {
 }
 
 func TestWriteError(t *testing.T) {
-	t.Parallel()
 	fName := "TestWriteError"
 	defer cleanup(fName)
 	writeOldFile(fName, t)
@@ -418,6 +389,9 @@ func TestWriteError(t *testing.T) {
 
 		return f, err
 	}
+	defer func() {
+		openFile = os.OpenFile
+	}()
 
 	err := Apply(bytes.NewReader(newFile), Options{TargetPath: fName})
 	if err == nil {