Test that the fejkdata binary without --seed draws a new seed each run

cmd/fejkdata/main_test.go

@@ -26,3 +26,22 @@ func TestMainRendersTheShippedData(t *testing.T) {
 		t.Errorf("fejkdata = %v, %q, %q, want SE followed by a last name and a locality", err, out, stderr.String())
 	}
 }
+
+func TestMainWithoutASeedDrawsANewSeedEachRun(t *testing.T) {
+	var outs [2]string
+	for i := range outs {
+		cmd := exec.Command(os.Args[0])
+		cmd.Env = append(os.Environ(), "FEJKDATA_RUN_MAIN=1")
+		cmd.Stdin = strings.NewReader("{uuid()}")
+		var stderr bytes.Buffer
+		cmd.Stderr = &stderr
+		out, err := cmd.Output()
+		if err != nil || len(out) == 0 {
+			t.Fatalf("fejkdata without --seed = %v, %q, %q", err, out, stderr.String())
+		}
+		outs[i] = string(out)
+	}
+	if outs[0] == outs[1] {
+		t.Errorf("two runs without --seed both printed %q, want a new seed each run", outs[0])
+	}
+}