junit: Add timestamp for suite start time

The junit schema defines this attribute on the testsuite.
In my case I need to import test results totally separate from the
testing pipeline since these are in two different systems. This
timestamp ensures the result processor puts the results into the right
time frame instead of assuming it just ran.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

internal/junitxml/report.go

@@ -31,6 +31,7 @@ type JUnitTestSuite struct {
 	Name       string          `xml:"name,attr"`
 	Properties []JUnitProperty `xml:"properties>property,omitempty"`
 	TestCases  []JUnitTestCase
+	Timestamp  string `xml:"timestamp,attr"`
 }
 
 // JUnitTestCase is a single test case with its result.
@@ -92,6 +93,7 @@ func generate(exec *testjson.Execution, cfg Config) JUnitTestSuites {
 			Properties: packageProperties(version),
 			TestCases:  packageTestCases(pkg, cfg.FormatTestCaseClassname),
 			Failures:   len(pkg.Failed),
+			Timestamp:  exec.Started().Format(time.RFC3339),
 		}
 		suites.Suites = append(suites.Suites, junitpkg)
 	}

testjson/execution.go

@@ -564,6 +564,10 @@ func (e *Execution) end() []TestEvent {
 	return result
 }
 
+func (e *Execution) Started() time.Time {
+	return e.started
+}
+
 // newExecution returns a new Execution and records the current time as the
 // time the test execution started.
 func newExecution() *Execution {