Tests for cycle-finding algorithm

tests/algo_test.cpp

@@ -0,0 +1,48 @@
+#define CATCH_CONFIG_ENABLE_PAIR_STRINGMAKER
+
+#include "cata_algo.h"
+
+#include "catch/catch.hpp"
+
+static void check_cycle_finding( std::unordered_map<int, std::vector<int>> &g,
+                                 std::vector<std::vector<int>> &expected )
+{
+    CAPTURE( g );
+    std::vector<std::vector<int>> loops = cata::find_cycles( g );
+    // Canonicalize the list of loops by rotating each to be lexicographically
+    // least and then sorting.
+    for( std::vector<int> &loop : loops ) {
+        auto min = std::min_element( loop.begin(), loop.end() );
+        std::rotate( loop.begin(), min, loop.end() );
+    }
+    std::sort( loops.begin(), loops.end() );
+    CHECK( loops == expected );
+}
+
+
+TEST_CASE( "find_cycles_small" )
+{
+    std::unordered_map<int, std::vector<int>> g = {
+        { 0, { 1 } },
+        { 1, { 0 } },
+    };
+    std::vector<std::vector<int>> expected = {
+        { 0, 1 },
+    };
+    check_cycle_finding( g, expected );
+}
+TEST_CASE( "find_cycles" )
+{
+    std::unordered_map<int, std::vector<int>> g = {
+        { 0, { 0, 1 } },
+        { 1, { 0, 2, 3, 17 } },
+        { 2, { 1 } },
+        { 3, {} },
+    };
+    std::vector<std::vector<int>> expected = {
+        { 0 },
+        { 0, 1 },
+        { 1, 2 },
+    };
+    check_cycle_finding( g, expected );
+}