add SetTestTimeout for TestActivityEnvironment (#484)

* add SetTestTimeout for TestActivityEnvironment

* update doc

Author: yiminc

internal/workflow_testsuite.go

@@ -158,6 +158,13 @@ func (t *TestActivityEnvironment) SetWorkerOptions(options WorkerOptions) *TestA
 	return t
 }
 
+// SetTestTimeout sets the wall clock timeout for this activity test run. When test timeout happen, it means activity is
+// taking too long.
+func (t *TestActivityEnvironment) SetTestTimeout(idleTimeout time.Duration) *TestActivityEnvironment {
+	t.impl.testTimeout = idleTimeout
+	return t
+}
+
 // SetStartTime sets the start time of the workflow. This is optional, default start time will be the wall clock time when
 // workflow starts. Start time is the workflow.Now(ctx) time at the beginning of the workflow.
 func (t *TestWorkflowEnvironment) SetStartTime(startTime time.Time) {