JLCEL Course

PC04-L03 · guided challenge

One delivery method

Require a pickup location or a shipping address, but not both.

Practical CEL4 test casesDocumented
What will I practise?

You can use inequality between two booleans to express exactly one option.

How is it checked?

Your one expression must produce the expected result for all four JSON inputs.

When am I done?

When all tests pass and you can explain every condition in your expression.

Word problem

A request must contain exactly one delivery method: a pickup location or a shipping address.

Exact requirements

  1. Pickup only is valid.
  2. Shipping only is valid.
  3. Both present is invalid.
  4. Both missing is invalid.

Required result

Write one CEL expression. It must return the expected value and type for all four prepared JSON inputs. Do not change the inputs to make an incomplete expression pass.

Recommended procedure

  1. Translate each numbered requirement into one small boolean condition.
  2. Run the starter expression and inspect which cases fail.
  3. Add one condition at a time and run the complete suite again.
  4. Mark the challenge complete only when you can explain every operator and every boundary.

Solve the challenge · browser test suite

Write one expression that passes every case

Edit the CEL expression, then run it against all prepared JSON inputs. A solution is complete only when every case passes.

4 test cases

Hint: The || operator also accepts both options. You need true only when presence differs.

Tip: press Ctrl/⌘ + Enter to run all tests.
PickupNot run yet
Expected: true · bool
Show JSON input
{
  "request": {
    "pickupLocation": "BA-01"
  }
}
Shipping addressNot run yet
Expected: true · bool
Show JSON input
{
  "request": {
    "shippingAddress": "Main 1"
  }
}
Both methodsNot run yet
Expected: false · bool
Show JSON input
{
  "request": {
    "pickupLocation": "BA-01",
    "shippingAddress": "Main 1"
  }
}
No methodNot run yet
Expected: false · bool
Show JSON input
{
  "request": {}
}
Test result

Not run yet

The same expression runs against every case. Test data is fixed so that boundary and failure scenarios cannot be skipped.

Explained solution

Show the complete expression
has(request.pickupLocation) != has(request.shippingAddress)

Why the solution works

  1. Each has() returns one presence boolean.
  2. The rule needs true only when the two booleans differ.
  3. != expresses that difference directly.
  4. Using || would incorrectly accept the case where both are present.

What the test cases prove

  • Pickup: expected true (bool).
  • Shipping address: expected true (bool).
  • Both methods: expected false (bool).
  • No method: expected false (bool).

The cases are intentionally different. A solution that passes only the first case has not yet implemented the complete rule.

Common mistake

Do not optimise the expression for the first successful input. A requirement is implemented only when its positive case, negative case, and boundary case all produce the stated result.

Knowledge check

Can you point to the exact part of the solution that makes each false test case fail? If two different failures depend on the same condition, explain why.

Key takeaway

You can use inequality between two booleans to express exactly one option.

Sources

  • CEL-DEV — official CEL overview.
  • CEL-LANG — official CEL language definition for operators, types, macros, presence, strings, and time values used in this challenge.