Add e2e tests

e2e/validation_extra_test.go

@@ -0,0 +1,13 @@
+package e2e
+
+import (
+	"testing"
+)
+
+func TestValidation_ConcurrencyExceedsMax(t *testing.T) {
+	t.Parallel()
+
+	res := run("-U", "http://example.com", "-r", "1", "-q", "-c", "200000000")
+	assertExitCode(t, res, 1)
+	assertContains(t, res.Stderr, "concurrency must not exceed 100,000,000")
+}