1 files changed, 87 insertions, 0 deletions
diff --git a/container-di/src/test/java/com/yahoo/container/di/componentgraph/cycle/CycleFinderTest.java b/container-di/src/test/java/com/yahoo/container/di/componentgraph/cycle/CycleFinderTest.java
new file mode 100644
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+++ b/container-di/src/test/java/com/yahoo/container/di/componentgraph/cycle/CycleFinderTest.java
@@ -0,0 +1,87 @@
+/*
+ * Copyright 2019 Oath Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+ */
+
+package com.yahoo.container.di.componentgraph.cycle;
+
+import org.junit.Test;
+
+import static com.yahoo.container.di.componentgraph.cycle.CycleFinderTest.Vertices.A;
+import static com.yahoo.container.di.componentgraph.cycle.CycleFinderTest.Vertices.B;
+import static com.yahoo.container.di.componentgraph.cycle.CycleFinderTest.Vertices.C;
+import static com.yahoo.container.di.componentgraph.cycle.CycleFinderTest.Vertices.D;
+import static org.hamcrest.Matchers.contains;
+import static org.hamcrest.Matchers.empty;
+import static org.junit.Assert.assertThat;
+
+/**
+ * @author gjoranv
+ */
+public class CycleFinderTest {
+
+    enum Vertices {A, B, C, D}
+
+    @Test
+    public void graph_without_cycles_returns_no_cycle() {
+        var graph = new Graph<Vertices>();
+        graph.edge(A, B);
+        graph.edge(B, C);
+        graph.edge(A, C);
+        graph.edge(D, A);
+
+        var cycleFinder = new CycleFinder<>(graph);
+        assertThat(cycleFinder.findCycle(), empty());
+    }
+
+    @Test
+    public void graph_with_cycle_returns_cycle() {
+        var graph = new Graph<Vertices>();
+        graph.edge(A, B);
+        graph.edge(B, C);
+        graph.edge(C, A);
+
+        var cycleFinder = new CycleFinder<>(graph);
+        assertThat(cycleFinder.findCycle(), contains(A, B, C, A));
+    }
+
+    @Test
+    public void graph_with_self_referencing_vertex_returns_cycle() {
+        var graph = new Graph<Vertices>();
+        graph.edge(A, A);
+
+        var cycleFinder = new CycleFinder<>(graph);
+        assertThat(cycleFinder.findCycle(), contains(A, A));
+    }
+
+    @Test
+    public void leading_nodes_are_stripped_from_cycle() {
+        var graph = new Graph<Vertices>();
+        graph.edge(A, B);
+        graph.edge(B, C);
+        graph.edge(C, B);
+
+        var cycleFinder = new CycleFinder<>(graph);
+        assertThat(cycleFinder.findCycle(), contains(B, C, B));
+    }
+
+    @Test
+    public void findCycle_is_idempotent_with_cycle() {
+        var graph = new Graph<Vertices>();
+        graph.edge(A, A);
+
+        var cycleFinder = new CycleFinder<>(graph);
+        assertThat(cycleFinder.findCycle(), contains(A, A));
+        assertThat(cycleFinder.findCycle(), contains(A, A));
+    }
+
+    @Test
+    public void findCycle_is_idempotent_without_cycle() {
+        var graph = new Graph<Vertices>();
+        graph.edge(A, B);
+
+        var cycleFinder = new CycleFinder<>(graph);
+        assertThat(cycleFinder.findCycle(), empty());
+        assertThat(cycleFinder.findCycle(), empty());
+    }
+
+}