Add (failing) tests to detect negative cycles

Author: Christian Lück

tests/DetectNegativeCycleTest.php

@@ -0,0 +1,151 @@
+<?php
+
+use Fhaculty\Graph\Graph;
+use Fhaculty\Graph\Algorithm\DetectNegativeCycle;
+
+class DetectNegativeCycleTest extends TestCase
+{
+    public function testNullGraph()
+    {
+        $graph = new Graph();
+
+        $alg = new DetectNegativeCycle($graph);
+
+        $this->assertFalse($alg->hasCycleNegative());
+
+        return $alg;
+    }
+
+    /**
+     *
+     * @param DetectNegativeCycle $alg
+     * @depends testNullGraph
+     * @expectedException UnderflowException
+     */
+    public function testNullGraphHasNoCycle(DetectNegativeCycle $alg)
+    {
+        $alg->getCycleNegative();
+    }
+
+    /**
+     *
+     * @param DetectNegativeCycle $alg
+     * @depends testNullGraph
+     * @expectedException UnderflowException
+     */
+    public function testNullGraphHasNoCycleGraph(DetectNegativeCycle $alg)
+    {
+        $alg->createGraph();
+    }
+
+    public function testNegativeLoop()
+    {
+        // 1 --[-1]--> 1
+        $graph = new Graph();
+        $v1 = $graph->createVertex(1);
+        $e1 = $v1->createEdgeTo($v1)->setWeight(-1);
+
+        $alg = new DetectNegativeCycle($graph);
+
+        $this->assertTrue($alg->hasCycleNegative());
+
+        $cycle = $alg->getCycleNegative();
+
+        $this->assertCount(1, $cycle->getEdges());
+        $this->assertCount(2, $cycle->getVertices());
+        $this->assertEquals($e1, $cycle->getEdges()->getEdgeFirst());
+        $this->assertEquals($v1, $cycle->getVertices()->getVertexFirst());
+    }
+
+    public function testNegativeCycle()
+    {
+        // 1 --[-1]--> 2
+        // ^           |
+        // \---[-2]----/
+        $graph = new Graph();
+        $v1 = $graph->createVertex(1);
+        $v2 = $graph->createVertex(2);
+        $e1 = $v1->createEdgeTo($v2)->setWeight(-1);
+        $e2 = $v2->createEdgeTo($v1)->setWeight(-2);
+
+        $alg = new DetectNegativeCycle($graph);
+
+        $this->assertTrue($alg->hasCycleNegative());
+
+        $cycle = $alg->getCycleNegative();
+
+        $this->assertCount(2, $cycle->getEdges());
+        $this->assertCount(3, $cycle->getVertices());
+    }
+
+    public function testNegativeUndirectedIsNegativeCycle()
+    {
+        // 1 --[-1]-- 2
+        $graph = new Graph();
+        $v1 = $graph->createVertex(1);
+        $v2 = $graph->createVertex(2);
+        $e1 = $v1->createEdge($v2)->setWeight(-1);
+
+        $alg = new DetectNegativeCycle($graph);
+
+        $this->assertTrue($alg->hasCycleNegative());
+
+        $cycle = $alg->getCycleNegative();
+
+        $this->assertCount(2, $cycle->getEdges());
+        $this->assertCount(3, $cycle->getVertices());
+    }
+
+    public function testNegativeCycleSubgraph()
+    {
+        // 1 --[1]--> 2 --[1]--> 3 --[1]--> 4
+        //                       ^          |
+        //                       \---[-2]---/
+        $graph = new Graph();
+        $v1 = $graph->createVertex(1);
+        $v2 = $graph->createVertex(2);
+        $v3 = $graph->createVertex(3);
+        $v4 = $graph->createVertex(4);
+        $e1 = $v1->createEdgeTo($v2)->setWeight(1);
+        $e2 = $v2->createEdgeTo($v3)->setWeight(1);
+        $e3 = $v3->createEdgeTo($v4)->setWeight(1);
+        $e4 = $v4->createEdgeTo($v3)->setWeight(-2);
+
+        $alg = new DetectNegativeCycle($graph);
+
+        $this->assertTrue($alg->hasCycleNegative());
+
+        $cycle = $alg->getCycleNegative();
+
+        $this->assertCount(2, $cycle->getEdges());
+        $this->assertCount(3, $cycle->getVertices());
+        $this->assertTrue($cycle->getVertices()->hasVertexId(3));
+        $this->assertTrue($cycle->getVertices()->hasVertexId(4));
+    }
+
+    public function testNegativeComponents()
+    {
+        // 1 -- 2     3 --[-1]--> 4
+        //            ^           |
+        //            \---[-2]----/
+        $graph = new Graph();
+        $v1 = $graph->createVertex(1);
+        $v2 = $graph->createVertex(2);
+        $v3 = $graph->createVertex(3);
+        $v4 = $graph->createVertex(4);
+        $e1 = $v1->createEdge($v2);
+        $e2 = $v3->createEdgeTo($v4)->setWeight(-1);
+        $e3 = $v4->createEdgeTo($v3)->setWeight(-2);
+
+        $alg = new DetectNegativeCycle($graph);
+
+        $this->assertTrue($alg->hasCycleNegative());
+
+        $cycle = $alg->getCycleNegative();
+
+        $this->assertCount(2, $cycle->getEdges());
+        $this->assertCount(3, $cycle->getVertices());
+        $this->assertTrue($cycle->getVertices()->hasVertexId(3));
+        $this->assertTrue($cycle->getVertices()->hasVertexId(4));
+    }
+}