fixup fixture logic

There was a bug with init() but it was resolved in
https://github.com/bazelbuild/rules_go/pull/2696

Changed to match other fixture methods.

Change-Id: I882b8535e5c5c117fb10c41d34c8eed1ccdb74bb

staging/src/k8s.io/legacy-cloud-providers/vsphere/vclib/fixtures/fixtures.go

@@ -17,10 +17,10 @@ limitations under the License.
 package fixtures
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 	"runtime"
-	"strings"
 )
 
 var (
@@ -38,24 +38,9 @@ var (
 )
 
 func init() {
-	_, thisFile, _, ok := runtime.Caller(0)
+	fixturesDir, err := pkgPath()
-	if !ok {
-		panic("Cannot get path to the fixtures")
-	}
-
-	fixturesDir := filepath.Dir(thisFile)
-
-	cwd, err := os.Getwd()
 	if err != nil {
-		panic("Cannot get CWD: " + err.Error())
+		panic(fmt.Sprintf("Cannot get path to the fixtures: %s", err))
-	}
-
-	// When tests run in a bazel sandbox `runtime.Caller()`
-	// returns a relative path, when run with plain `go test` the path
-	// returned is absolute. To make those fixtures work in both those cases,
-	// we prepend the CWD iff the CWD is not yet part of the path to the fixtures.
-	if !strings.HasPrefix(fixturesDir, cwd) {
-		fixturesDir = filepath.Join(cwd, fixturesDir)
 	}
 
 	CaCertPath = filepath.Join(fixturesDir, "ca.pem")
@@ -63,3 +48,33 @@ func init() {
 	ServerKeyPath = filepath.Join(fixturesDir, "server.key")
 	InvalidCertPath = filepath.Join(fixturesDir, "invalid.pem")
 }
+
+// pkgPath returns the absolute file path to this package's directory. With go
+// test, we can just look at the runtime call stack. However, bazel compiles go
+// binaries with the -trimpath option so the simple approach fails however we
+// can consult environment variables to derive the path.
+//
+// The approach taken here works for both go test and bazel on the assumption
+// that if and only if trimpath is passed, we are running under bazel.
+func pkgPath() (string, error) {
+	_, thisFile, _, ok := runtime.Caller(1)
+	if !ok {
+		return "", fmt.Errorf("failed to get current file")
+	}
+
+	pkgPath := filepath.Dir(thisFile)
+
+	// If we find bazel env variables, then -trimpath was passed so we need to
+	// construct the path from the environment.
+	if testSrcdir, testWorkspace := os.Getenv("TEST_SRCDIR"), os.Getenv("TEST_WORKSPACE"); testSrcdir != "" && testWorkspace != "" {
+		pkgPath = filepath.Join(testSrcdir, testWorkspace, pkgPath)
+	}
+
+	// If the path is still not absolute, something other than bazel compiled
+	// with -trimpath.
+	if !filepath.IsAbs(pkgPath) {
+		return "", fmt.Errorf("can't construct an absolute path from %q", pkgPath)
+	}
+
+	return pkgPath, nil
+}