add instrumentation test helpers

[#75375442]

Signed-off-by: Joseph Rodriguez <jrodriguez@pivotallabs.com>

cfcomponent/instrumentation/testhelpers/testhelpers.go

@@ -0,0 +1,19 @@
+package testhelpers
+
+import "github.com/cloudfoundry/loggregatorlib/cfcomponent/instrumentation"
+import . "github.com/onsi/gomega"
+
+func MetricValue(instrumentable instrumentation.Instrumentable, name string) interface{} {
+	for _, metric := range instrumentable.Emit().Metrics {
+		if metric.Name == name {
+			return metric.Value
+		}
+	}
+	return nil
+}
+
+func EventuallyExpectMetric(instrumentable instrumentation.Instrumentable, name string, value uint64) {
+	Eventually(func() interface{} {
+		return MetricValue(instrumentable, name)
+	}).Should(Equal(value))
+}