Justin Visser
736cd9070d
One random threshold per DIRECTED edge, drawn once per world: scenarios sharing thresholds differ only in who is educated, the prototype's 'same world, different lever' trick. The cascade is plain BFS in rounds; an educated student receives the fake but never forwards it, which is the entire effect of the lever. The result stores the first-reached round per node (exactly what a frontend animation needs). Tests hand-craft a 4-node line graph with exact thresholds, so every expectation is exact: spread, directional blocking, educated cutoff.
102 lines
3.1 KiB
Go
102 lines
3.1 KiB
Go
package engine
|
|
|
|
import (
|
|
"slices"
|
|
"testing"
|
|
)
|
|
|
|
// The cascade is deterministic once thresholds are fixed, so these tests
|
|
// hand-craft a tiny line graph (0-1-2-3) and exact thresholds: no
|
|
// randomness, every expectation is exact.
|
|
|
|
func lineGraph(numNodes int) *Graph {
|
|
graph := NewGraph(numNodes)
|
|
for node := 0; node < numNodes-1; node++ {
|
|
graph.AddEdge(node, node+1)
|
|
}
|
|
return graph
|
|
}
|
|
|
|
// uniformThresholds gives every directed edge the same threshold.
|
|
func uniformThresholds(graph *Graph, value float64) EdgeThresholds {
|
|
thresholds := make(EdgeThresholds)
|
|
for node := range graph.NumNodes() {
|
|
for _, neighbor := range graph.Neighbors(node) {
|
|
thresholds[[2]int{node, neighbor}] = value
|
|
}
|
|
}
|
|
return thresholds
|
|
}
|
|
|
|
func TestRunCascadeSpreadsAlongOpenEdges(t *testing.T) {
|
|
graph := lineGraph(4)
|
|
thresholds := uniformThresholds(graph, 0.1) // 0.1 < 0.5: every edge forwards
|
|
|
|
result := RunCascade(graph, 0, 0.5, nil, thresholds)
|
|
|
|
wantRounds := []int{0, 1, 2, 3} // one hop further each round
|
|
if !slices.Equal(result.ReachedAtRound, wantRounds) {
|
|
t.Errorf("ReachedAtRound = %v, want %v", result.ReachedAtRound, wantRounds)
|
|
}
|
|
if result.NumReached != 4 {
|
|
t.Errorf("NumReached = %d, want 4", result.NumReached)
|
|
}
|
|
if result.NumRounds != 4 {
|
|
t.Errorf("NumRounds = %d, want 4", result.NumRounds)
|
|
}
|
|
}
|
|
|
|
func TestRunCascadeThresholdBlocksOneDirection(t *testing.T) {
|
|
graph := lineGraph(4)
|
|
thresholds := uniformThresholds(graph, 0.1)
|
|
// Close the 1 -> 2 direction only. The open 2 -> 1 direction must not
|
|
// matter: student 2 never gets the fake, so never forwards anything.
|
|
thresholds[[2]int{1, 2}] = 0.9
|
|
|
|
result := RunCascade(graph, 0, 0.5, nil, thresholds)
|
|
|
|
wantRounds := []int{0, 1, NeverReached, NeverReached}
|
|
if !slices.Equal(result.ReachedAtRound, wantRounds) {
|
|
t.Errorf("ReachedAtRound = %v, want %v", result.ReachedAtRound, wantRounds)
|
|
}
|
|
if result.NumReached != 2 {
|
|
t.Errorf("NumReached = %d, want 2", result.NumReached)
|
|
}
|
|
}
|
|
|
|
func TestRunCascadeEducatedReceivesButDoesNotForward(t *testing.T) {
|
|
graph := lineGraph(4)
|
|
thresholds := uniformThresholds(graph, 0.1)
|
|
|
|
result := RunCascade(graph, 0, 0.5, []int{1}, thresholds)
|
|
|
|
// Student 1 is educated: still receives the fake in round 1, but the
|
|
// chain stops there.
|
|
wantRounds := []int{0, 1, NeverReached, NeverReached}
|
|
if !slices.Equal(result.ReachedAtRound, wantRounds) {
|
|
t.Errorf("ReachedAtRound = %v, want %v", result.ReachedAtRound, wantRounds)
|
|
}
|
|
}
|
|
|
|
func TestNewEdgeThresholdsDeterministicAndComplete(t *testing.T) {
|
|
graph, err := HolmeKim(30, 3, 0.45, newRand(17))
|
|
if err != nil {
|
|
t.Fatal(err)
|
|
}
|
|
|
|
first := NewEdgeThresholds(graph, newRand(2))
|
|
second := NewEdgeThresholds(graph, newRand(2))
|
|
|
|
if wantSize := 2 * graph.NumEdges(); len(first) != wantSize {
|
|
t.Errorf("len(thresholds) = %d, want %d (two directions per edge)", len(first), wantSize)
|
|
}
|
|
for directedEdge, firstDraw := range first {
|
|
if firstDraw < 0 || firstDraw >= 1 {
|
|
t.Errorf("threshold %v = %v, want in [0, 1)", directedEdge, firstDraw)
|
|
}
|
|
if secondDraw := second[directedEdge]; firstDraw != secondDraw {
|
|
t.Errorf("threshold %v differs across identical seeds: %v != %v",
|
|
directedEdge, firstDraw, secondDraw)
|
|
}
|
|
}
|
|
}
|