Adding first version of HealthCheck

Added a expvar style handler for the debug http server to allow health checks (/debug/health).

Signed-off-by: Diogo Monica <diogo@docker.com>

health/health_test.go

@@ -0,0 +1,47 @@
+package health
+
+import (
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// TestReturns200IfThereAreNoChecks ensures that the result code of the health
+// endpoint is 200 if there are not currently registered checks.
+func TestReturns200IfThereAreNoChecks(t *testing.T) {
+	recorder := httptest.NewRecorder()
+
+	req, err := http.NewRequest("GET", "https://fakeurl.com/debug/health", nil)
+	if err != nil {
+		t.Errorf("Failed to create request.")
+	}
+
+	StatusHandler(recorder, req)
+
+	if recorder.Code != 200 {
+		t.Errorf("Did not get a 200.")
+	}
+}
+
+// TestReturns500IfThereAreErrorChecks ensures that the result code of the
+// health endpoint is 500 if there are health checks with errors
+func TestReturns503IfThereAreErrorChecks(t *testing.T) {
+	recorder := httptest.NewRecorder()
+
+	req, err := http.NewRequest("GET", "https://fakeurl.com/debug/health", nil)
+	if err != nil {
+		t.Errorf("Failed to create request.")
+	}
+
+	// Create a manual error
+	Register("some_check", CheckFunc(func() error {
+		return errors.New("This Check did not succeed")
+	}))
+
+	StatusHandler(recorder, req)
+
+	if recorder.Code != 503 {
+		t.Errorf("Did not get a 503.")
+	}
+}