karatelabs/karate · error · AssertionError

assert failed:

Error message

assert failed: 

What it means

Karate's 'assert' step evaluates its text as an expression; if the resulting boolean is false, an AssertionError labeled 'assert failed: <expression>' is thrown. This is an intentional assertion failure, not a bug — the JS expression evaluated to false.

Solutions

1. Print the values involved (print responseStatus, myVar) to see actual vs expected
2. Fix the expectation if the product behavior is correct, or fix the underlying bug/fixture if not
3. Watch for type mismatches — compare with explicit conversions when values come from JSON strings
4. Ensure referenced variables are defined earlier (undefined comparisons often evaluate false)

Example fix

// before: fails when status is 201
assert responseStatus == 200
// after: accept both success codes
assert responseStatus == 200 || responseStatus == 201

// log operands before asserting on them
print('responseStatus:', responseStatus, 'expected:', 200);
// assert responseStatus == 200

// AssertionError is intentional; let it propagate and read the labeled expression
try { executor.execute(step); } catch (AssertionError e) { report.stepFailed(step, e.getMessage()); throw e; }

When it happens

Trigger: An 'assert' step in a feature whose expression returns false, e.g. 'assert responseStatus == 200' after a non-200 response, or 'assert myVar.length == 3' with a different length.

Common situations: API regression caught by the test (wrong status code, wrong computed value); type coercion surprises making the expression false (string '5' vs number 5); evaluating against undefined variables which yield false-y comparisons.

Related errors

• assert expression must return boolean:
• append() needs at least two arguments
• appendTo() needs at least two arguments: list and item(s)
• call with tag selector requires a feature context
• called feature failed

AI-assisted analysis of karatelabs/karate@a22eb90246 (2026-09-12). Data as JSON: /api/errors/aab76cebc928d7e5. Report an issue: GitHub.

Appendix: source

Thrown at karate-core/src/main/java/io/karatelabs/core/StepExecutor.java:1902

        return value;
    }

    /**
     * True for an expression like {@code ({ a: 1 })} or {@code ([1, 2])} — a JSON literal
     * the user forced through JS evaluation by wrapping it in round brackets.
     */
    private static boolean isParenWrappedJson(String expr) {
        if (expr.length() < 3 || expr.charAt(0) != '(' || expr.charAt(expr.length() - 1) != ')') {
            return false;
        }
        return StringUtils.looksLikeJson(expr.substring(1, expr.length() - 1).trim());
    }

    private void executeAssert(Step step) {
        Object result = runtime.eval(step.getText());
        if (result instanceof Boolean b) {
            if (!b) {
                throw new AssertionError(withCommentLabel(step, "assert failed: " + step.getText()));
            }
        } else {
            throw new RuntimeException("assert expression must return boolean: " + step.getText());
        }
    }

    private static final LogContext.LogWriter SCENARIO_LOG = LogContext.with(LogContext.SCENARIO_LOGGER);

    private void executePrint(Step step) {
        // Wrap in array to handle comma-separated expressions like: print 'foo', 'bar'
        // Without wrapping, JS comma operator would return only the last value
        Object value = runtime.eval("[" + step.getText() + "]");
        if (value instanceof List<?> list) {
            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < list.size(); i++) {
                if (i > 0) {
                    sb.append(' ');
                }

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