Table-driven unit tests

Here is the code we want to test.

package search

// Find returns the smallest index i at which x <= a[i].
// If there is no such index, it returns len(a).
// The slice must be sorted in ascending order.
func Find(a []int, x int) int {
	switch len(a) {
	case 0:
		return 0
	case 1:
		if x <= a[0] {
			return 0
		}
		return 1
	}
	mid := len(a) / 2
	if x <= a[mid-1] {
		return Find(a[:mid], x)
	}
	return mid + Find(a[mid:], x)
}

• Put the test code in a file whose name ends with _test.go.
• Write a function TestXXX with a single argument of type *testing.T. The test framework runs each such function.
• To indicate a failed test, call a failure function such as t.Errorf.

package search

import "testing"

var tests = []struct {
	a   []int
	x   int
	exp int
}{
	{[]int{}, 1, 0},
	{[]int{1, 2, 3, 3}, 0, 0},
	{[]int{1, 2, 3, 3}, 1, 0},
	{[]int{1, 2, 3, 3}, 2, 1},
	{[]int{1, 2, 3, 3}, 3, 3}, // incorrect test case
	{[]int{1, 2, 3, 3}, 4, 4},
}

func TestFind(t *testing.T) {
	for _, e := range tests {
		res := Find(e.a, e.x)
		if res != e.exp {
			t.Errorf("Find(%v, %d) = %d, expected %d",
				e.a, e.x, res, e.exp)
		}
	}
}

Run the tests with go test.

$ go test
--- FAIL: TestFind (0.00s)
	search_test.go:22: Find([1 2 3 3], 3) = 2, expected 3
FAIL
exit status 1
FAIL	.../search	0.001s

Further reading

The Induction and recursive functions article has a correctness proof for the Find function.

More code examples

Go blueprints: code for com­mon tasks is a collection of handy code examples.

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