Testing and Debugging

Testing with the SDK

Inline execution

The fastest way to test Zymba code:

Bash

zeysdk run --zymba '$x = 42; echo $x * 2;'

The output includes execution metrics:

Text

Metrics
  Load Time      | 0.8 ms
  Execution Time | 0.1 ms
  Memory Usage   | 436.28 KB
  Output Size    | 2 Bytes
Output
  84

Testing functions

Test individual functions in isolation:

Bash

zeysdk run --zymba '
function $calculateDiscount($price, $percent) {
    if ($percent < 0 || $percent > 100) {
        throw new @Exception("Invalid discount");
    }
    return $price * (1 - $percent / 100);
}

echo $calculateDiscount(100, 15);
echo " ";
echo $calculateDiscount(200, 25);
'

Testing error paths

Verify that error handling works correctly:

Bash

zeysdk run --zymba '
try {
    $data = @Var.fromJSON("invalid json");
    echo "Should not reach here";
} catch ($e) {
    echo "Caught: " . $e.getMessage();
}
'

---

Debugging techniques

Echo debugging

The simplest approach — output values at key points:

ZYMBA

$data = @Var.fromJSON($input);
echo "Parsed data: " . @Var.toJSON($data) . "\n";

$filtered = @Array.filter($data.items, function($item) {
    return $item.active;
});
echo "Filtered count: " . count $filtered . "\n";

@Console.log

Use @Console.log() for structured debug output that doesn't interfere with the HTTP response body:

ZYMBA

@Console.log("Processing order", $orderId);
@Console.log("Items:", @Var.toJSON($items));

// Retrieve collected messages
$messages = @Console.listMessages();
$summary  = @Console.getSummary();

Type inspection

When a value behaves unexpectedly, inspect its type:

ZYMBA

$value = $getData();

echo "Type: "     . typeof $value . "\n";
echo "Is object: " . ($value is object) . "\n";
echo "Is null: "   . ($value is null) . "\n";
echo "Empty: "     . (empty $value) . "\n";
echo "Exists: "    . (exists $value) . "\n";

if ($value is object) {
    echo "Keys: " . @Var.toJSON(@Array.listKeys($value)) . "\n";
}

@Var.toSource

Get a complete, human-readable representation of any value, including nested structures:

ZYMBA

$complex = [a: [1, 2], b: [x: "hello"]];
echo @Var.toSource($complex);

Stack traces

Exception objects include stack traces for debugging:

ZYMBA

try {
    $riskyOperation();
} catch ($e) {
    echo "Error: " . $e.getMessage() . "\n";
    echo "Trace: " . $e.getTracesAsString() . "\n";
}

---

Test patterns

Assertion helper

Build a simple assertion function:

ZYMBA

function $assert($condition, $message = "Assertion failed") {
    unless ($condition) {
        throw new @Exception($message);
    }
}

function $assertEqual($actual, $expected, $label = "") {
    if ($actual !== $expected) {
        throw new @Exception(
            "assertEqual failed" . ($label ? " ($label)" : "")
            . ": expected " . @Var.toJSON($expected)
            . " but got "   . @Var.toJSON($actual)
        );
    }
}

// Usage
$assertEqual(1 + 1, 2, "basic math");
$assertEqual(@String.trim("  hi  "), "hi", "trim");
$assertEqual(@Array.count([1,2,3]), 3, "count");
echo "All tests passed";

Test runner pattern

Organize tests into named test cases:

ZYMBA

$tests = [
    "string trim": function() {
        $assertEqual(@String.trim("  hello  "), "hello");
    },
    "array sort": function() {
        $result = @Array.sortAscByValues([3, 1, 2]);
        $assertEqual(@Array.firstValue($result), 1);
    },
    "json roundtrip": function() {
        $data   = [name: "test", value: 42];
        $json   = @Var.toJSON($data);
        $parsed = @Var.fromJSON($json);
        $assertEqual($parsed.name, "test");
        $assertEqual($parsed.value, 42);
    }
];

$passed = 0;
$failed = 0;

for ($tests as $name: $test) {
    try {
        $test();
        $passed++;
        echo "PASS: $name\n";
    } catch ($e) {
        $failed++;
        echo "FAIL: $name - " . $e.getMessage() . "\n";
    }
}

echo "\n$passed passed, $failed failed\n";

Testing with mock data

When testing code that normally queries a database, provide mock data:

ZYMBA

// Instead of:
// $users = $db.fetchAll(@SQL.prepare("SELECT * FROM contacts WHERE status = ?", 1), true);

// Use mock data for testing:
$users = [
    [ID: 1, name: "Alice", email: "[email protected]", status: 1],
    [ID: 2, name: "Bob",   email: "[email protected]",   status: 0],
    [ID: 3, name: "Charlie", email: "[email protected]", status: 1]
];

$active = @Array.filter($users, function($u) { return $u.status == 1; });
$assertEqual(count $active, 2, "should have 2 active users");

---

Common bugs and fixes

Bug: using + for string concatenation

ZYMBA

// Bug: produces 0 (numeric addition of non-numeric strings)
$msg = "Error: " + $detail;

// Fix: use . for concatenation
$msg = "Error: " . $detail;

Bug: missing $this in methods

ZYMBA

// Bug: creates a local variable, doesn't update the object
$Counter = new object() {
    value = 0;
    increment() {
        $value++;  // Wrong!
    }
};

// Fix: use $this
$Counter = new object() {
    value = 0;
    increment() {
        $this.value++;
    }
};

Bug: missing use in closures

ZYMBA

// Bug: $threshold is undefined inside the closure
$threshold = 100;
$isExpensive = function($p) { return $p > $threshold; };

// Fix: capture with use
$isExpensive = function($p) use ($threshold) { return $p > $threshold; };

Bug: expecting use to capture by reference

use copies the value at the time the closure is created. Mutations inside the closure don't affect the outer variable.

ZYMBA

// Bug: expects $total to accumulate
$total = 0;
@Array.forEach($items, function($item) use ($total) {
    $total += $item.price;  // Modifies local copy only
});
echo $total; // Still 0!

// Fix: use reduce instead
$total = @Array.reduce($items, 0, function($acc, $item) {
    return $acc + $item.price;
});

Bug: treating "0" as truthy

ZYMBA

// Bug: "0" is falsy in Zymba!
$value = "0";
if ($value) {
    // This block does NOT execute
}

// Fix: test explicitly for what you mean
if ($value !== null && $value !== "") {
    // This works for any non-empty, non-null value
}

---

Error handling best practices

Validate input early

ZYMBA

function $processOrder($input) {
    $order = null;
    try {
        $order = @Var.fromJSON($input);
    } catch ($e) {
        throw new @Exception("Invalid JSON input");
    }

    unless ($order is object) {
        throw new @Exception("Order must be an object");
    }
    unless (exists $order.items) {
        throw new @Exception("Order must have items");
    }
    if (empty $order.items) {
        throw new @Exception("Order items cannot be empty");
    }

    // All preconditions met — safe to process
}

Wrap external calls

ZYMBA

function $fetchExternalData($url) {
    try {
        $response = @HTTP.requestBody($url, "GET");
        return @Var.fromJSON($response);
    } catch ($e) {
        @Console.log("External API error: " . $e.getMessage());
        throw new @Exception("Failed to fetch data from external service");
    }
}

Clean up resources

Use finally to guarantee cleanup even when an exception is thrown:

ZYMBA

$tempFile = @IO.createTempFile("export");
try {
    @IO.writeCSV($tempFile, $data, ",");
    // ... process file
} finally {
    @IO.deleteIfExists($tempFile);
}

See also

• Best Practices — production patterns and conventions
• Exceptions — try/catch/finally in depth