Improve error behaviour of package coverage.

pkg/util/coverage/coverage.go

@@ -22,6 +22,7 @@ package coverage
 
 import (
 	"flag"
+	"fmt"
 	"github.com/golang/glog"
 	"k8s.io/apimachinery/pkg/util/wait"
 	"os"
@@ -29,8 +30,6 @@ import (
 	"time"
 )
 
-var flushInterval = 5 * time.Second
-
 var coverageFile string
 
 // tempCoveragePath returns a temporary file to write coverage information to.
@@ -48,9 +47,16 @@ func InitCoverage(name string) {
 	if coverageFile == "" {
 		coverageFile = "/tmp/k8s-" + name + ".cov"
 	}
-
-	if duration, err := time.ParseDuration(os.Getenv("KUBE_COVERAGE_FLUSH_INTERVAL")); err == nil {
-		flushInterval = duration
+	fmt.Println("Dumping coverage information to " + coverageFile)
+
+	flushInterval := 5 * time.Second
+	requestedInterval := os.Getenv("KUBE_COVERAGE_FLUSH_INTERVAL")
+	if requestedInterval != "" {
+		if duration, err := time.ParseDuration(requestedInterval); err == nil {
+			flushInterval = duration
+		} else {
+			panic("Invalid KUBE_COVERAGE_FLUSH_INTERVAL value; try something like '30s'.")
+		}
 	}
 
 	// Set up the unit test framework with the required arguments to activate test coverage.

pkg/util/coverage/coverage_disabled.go

@@ -18,9 +18,9 @@ limitations under the License.
 
 package coverage
 
-// InitCoverage is a no-op when not running with coverage.
+// InitCoverage is illegal when not running with coverage.
 func InitCoverage(name string) {
-
+	panic("Called InitCoverage when not built with coverage instrumentation.")
 }
 
 // FlushCoverage is a no-op when not running with coverage.