crowdsecurity/crowdsec · error

assertion '%s' is not a condition

Error message

assertion '%s' is not a condition

What it means

Run evaluates an assertion expression and expects the result to be a boolean. If the expr evaluation succeeds but the output is any other type (string, int, nil), the assertion cannot be interpreted as a pass/fail condition and this error is returned. It flags assertions written as expressions that return values rather than conditions.

Source

Thrown at pkg/hubtest/parser_assert.go:223

	ret, err := yaml.Marshal(output)
	if err != nil {
		return "", err
	}

	return string(ret), nil
}

func (p *ParserAssert) Run(assert string) (bool, error) {
	output, err := p.RunExpression(assert)
	if err != nil {
		return false, err
	}

	switch out := output.(type) {
	case bool:
		return out, nil
	default:
		return false, fmt.Errorf("assertion '%s' is not a condition", assert)
	}
}

func Escape(val string) string {
	val = strings.ReplaceAll(val, `\`, `\\`)
	val = strings.ReplaceAll(val, `"`, `\"`)

	return val
}

func (p *ParserAssert) AutoGenParserAssert() string {
	// attempt to autogen parser asserts
	ret := fmt.Sprintf("len(results) == %d\n", len(*p.TestData))

	// sort map keys for consistent order
	stages := maptools.SortedKeys(*p.TestData)

	for _, stage := range stages {

View on GitHub (pinned to 909b515798)

Solutions

1. Rewrite the assertion as a boolean condition (comparison, ==, !=, and/or)
2. Check that top-level expression returns bool, e.g. wrap value: Alert.GetValue() == '1.2.3.4'
3. Run the expression via EvalExpression to see the actual output type
4. Fix auto-generation artifacts if the assert file was machine produced

Example fix

// before
Alert.GetValue()
// after
Alert.GetValue() == '1.2.3.4'

out, err := p.RunExpression(assert)
if err != nil { return false, err }
if _, ok := out.(bool); !ok {
    return false, fmt.Errorf("assertion %q must evaluate to a bool, got %T", assert, out)
}

func isBool(v interface{}) bool { _, ok := v.(bool); return ok }

ok, err := p.Run(assertLine)
if err != nil {
    if strings.Contains(err.Error(), "is not a condition") {
        return fmt.Errorf("fix assertion to return a bool: %v", err)
    }
    return err
}

When it happens

Trigger: ParserAssert.Run called (by AssertFile) with an assertion whose expression evaluates to a non-bool, e.g. `Alert.GetValue()` alone, a string literal, or a comparison chain that expr reduces to a value.

Common situations: Assert files authored with bare expressions instead of equality/comparison conditions; auto-generated assertions after expr behavior changes; copy-pasted filter expressions into assert files.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• AverageInterval expects a slice of times
• groupby wrong type
• unexpected type %t (%v) while running '%s'
• invalid type for ip : %T
• element at index %d is not a time.Time

AI-assisted analysis of crowdsecurity/crowdsec@909b515798 (2026-09-06). Data as JSON: /api/errors/3cc0166e1094c940. Report an issue: GitHub.