Challenge 1 — Solution

Task: Write a function IsEven(n int) bool, then write a test file
with TestIsEven covering at least 3 cases (an even number, an odd
number, and zero) using t.Errorf for any mismatch.

// even.go
package main

func IsEven(n int) bool {
	return n%2 == 0
}

// even_test.go
package main

import "testing"

func TestIsEven(t *testing.T) {
	if !IsEven(4) {
		t.Errorf("IsEven(4) = false; want true")
	}

	if IsEven(7) {
		t.Errorf("IsEven(7) = true; want false")
	}

	if !IsEven(0) {
		t.Errorf("IsEven(0) = false; want true")
	}
}


Expected result of running "go test -v":

=== RUN   TestIsEven
--- PASS: TestIsEven (0.00s)
PASS

Notes:
- All three checks live inside ONE test function — t.Errorf records
  a failure but lets the function keep going, so all three checks
  still run even if an earlier one fails.
- 0 is correctly treated as even (0 % 2 == 0), matching the standard
  mathematical definition.
- The test file must end in _test.go and live in the same package as
  even.go for go test to discover it automatically.