fix(corpus-sweep): name every missing required flag, in flag order

cmd/internal-tools/corpus-sweep/main_test.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"io"
+	"strings"
+	"testing"
+)
+
+// Three flags missing is one rerun, not three: the operator is told about all
+// of them at once, in flag order, whatever order the check happened to walk.
+func TestParseArguments_NamesEveryMissingRequiredFlagInFlagOrder(t *testing.T) {
+	_, err := parseArguments(
+		[]string{"--spec", "s", "--max-steps", "10"},
+		io.Discard,
+	)
+	if err == nil {
+		t.Fatal("got no error, want every missing flag named")
+	}
+	message := err.Error()
+	previous := -1
+	for _, name := range []string{"--corpus", "--seeds", "--output"} {
+		at := strings.Index(message, name)
+		if at < 0 {
+			t.Fatalf("got %q, want %s named", message, name)
+		}
+		if at < previous {
+			t.Errorf("got %q, want the flags named in flag order", message)
+		}
+		previous = at
+	}
+	if strings.Contains(message, "--spec") {
+		t.Errorf("got %q, want the supplied --spec left out", message)
+	}
+}