Add unit test for closest

coder · Emyrk · May 30, 2023 · May 23, 2023 · May 23, 2023 · May 23, 2023
commit 1949217a53adadb0377b920f08a1a9e33c820fcb
diff --git a/coderd/metricscache/metrics_internal_test.go b/coderd/metricscache/metrics_internal_test.go
@@ -0,0 +1,92 @@
+package metricscache
+
+import (
+	"github.com/stretchr/testify/require"
+	"testing"
+)
+
+func TestClosest(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		Name     string
+		Keys     []int
+		Input    int
+		Expected int
+		NotFound bool
+	}{
+		{
+			Name:     "Empty",
+			Input:    10,
+			NotFound: true,
+		},
+		{
+			Name:     "Equal",
+			Keys:     []int{1, 2, 3, 4, 5, 6, 10, 12, 15},
+			Input:    10,
+			Expected: 10,
+		},
+		{
+			Name:     "ZeroOnly",
+			Keys:     []int{0},
+			Input:    10,
+			Expected: 0,
+		},
+		{
+			Name:     "NegativeOnly",
+			Keys:     []int{-10, -5},
+			Input:    10,
+			Expected: -5,
+		},
+		{
+			Name:     "CloseBothSides",
+			Keys:     []int{-10, -5, 0, 5, 8, 12},
+			Input:    10,
+			Expected: 8,
+		},
+		{
+			Name:     "CloseNoZero",
+			Keys:     []int{-10, -5, 5, 8, 12},
+			Input:    0,
+			Expected: -5,
+		},
+		{
+			Name:     "CloseLeft",
+			Keys:     []int{-10, -5, 0, 5, 8, 12},
+			Input:    20,
+			Expected: 12,
+		},
+		{
+			Name:     "CloseRight",
+			Keys:     []int{-10, -5, 0, 5, 8, 12},
+			Input:    -20,
+			Expected: -10,
+		},
+		{
+			Name:     "ChooseZero",
+			Keys:     []int{-10, -5, 0, 5, 8, 12},
+			Input:    2,
+			Expected: 0,
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.Name, func(t *testing.T) {
+			t.Parallel()
+
+			m := make(map[int]int)
+			for _, k := range tc.Keys {
+				m[k] = k
+			}
+
+			found, _, ok := closest(m, tc.Input)
+			if tc.NotFound {
+				require.False(t, ok, "should not be found")
+			} else {
+				require.True(t, ok)
+				require.Equal(t, tc.Expected, found, "closest")
+			}
+		})
+	}
+}
diff --git a/coderd/metricscache/metricscache.go b/coderd/metricscache/metricscache.go
@@ -375,10 +375,14 @@ func closest[V any](values map[int]V, offset int) (int, V, bool) {
 	var closestV V
 	diff := math.MaxInt
 	for k, v := range values {
-		if abs(k-offset) < diff {
+		newDiff := abs(k - offset)
+		// Take the closest value that is also the smallest value. We do this
+		// to make the output deterministic
+		if newDiff < diff || (newDiff == diff && k < closest) {
 			// new closest
 			closest = k
 			closestV = v
+			diff = newDiff
 		}
 	}
 	return closest, closestV, true