test: improved flaky test

Author: Luca Bianconi

Diff for: buildcache/build_cache_test.go

@@ -14,7 +14,8 @@ func Test_UpdateLastUsedFileNotExisting(t *testing.T) {
 	testBuildDir := paths.New(t.TempDir(), "sketches", "sketch-xxx")
 	err := os.MkdirAll(testBuildDir.String(), 0770)
 	require.Nil(t, err)
-	requireCorrectUpdate(t, testBuildDir)
+	timeBeforeUpdating := time.Unix(0, 0)
+	requireCorrectUpdate(t, testBuildDir, timeBeforeUpdating)
 }
 
 func Test_UpdateLastUsedFileExisting(t *testing.T) {
@@ -24,21 +25,22 @@ func Test_UpdateLastUsedFileExisting(t *testing.T) {
 	require.Nil(t, err)
 
 	// create the file
-	err = paths.New(testBuildDir.Join(lastUsedFileName).String()).WriteFile([]byte{})
+	preExistingFile := testBuildDir.Join(lastUsedFileName).String()
+	err = paths.New(preExistingFile).WriteFile([]byte{})
 	require.Nil(t, err)
-
-	requireCorrectUpdate(t, testBuildDir)
+	timeBeforeUpdating := time.Now().Add(-time.Second)
+	os.Chtimes(preExistingFile, time.Now(), timeBeforeUpdating)
+	requireCorrectUpdate(t, testBuildDir, timeBeforeUpdating)
 }
 
-func requireCorrectUpdate(t *testing.T, dir *paths.Path) {
-	timeBeforeUpdating := time.Now()
+func requireCorrectUpdate(t *testing.T, dir *paths.Path, prevModTime time.Time) {
 	err := UpdateLastUsedTime(dir)
 	require.Nil(t, err)
 	expectedFile := dir.Join(lastUsedFileName)
 	fileInfo, err := os.Stat(expectedFile.String())
 	require.Nil(t, err)
 
-	require.GreaterOrEqual(t, fileInfo.ModTime(), timeBeforeUpdating)
+	require.GreaterOrEqual(t, fileInfo.ModTime(), prevModTime)
 }
 
 func TestPurge(t *testing.T) {