Add new tests.

Author: Schwarf

data_structures/source/test/union_find_disjoint_set/test_union_find_dense.cpp

@@ -1,6 +1,140 @@
 //
 // Created by andreas on 02.02.23.
 //
+
+#include <gtest/gtest.h>
+#include <vector>
+#include <optional>
+
 #include "union_find_disjoint_set/union_find_dense.h"
 
+// Helper: connect all nodes in vec to vec[0]
+template <typename UnionFindType, typename T>
+static void UniteAll(UnionFindType& union_find, const std::vector<T>& vec)
+{
+    for (size_t i = 1; i < vec.size(); ++i)
+    {
+        union_find.union_set(vec[0], vec[i]);
+    }
+}
+
+TEST(UnionFindDense, InitiallyAllDisconnected)
+{
+    constexpr int elements{10};
+    UnionFindDense<int> union_find(elements);
+
+    for (int i{}; i < elements; ++i)
+    {
+        for (int j{}; j < elements; ++j)
+        {
+            if (i==j)
+                EXPECT_TRUE(union_find.are_connected(i, j));
+            else
+                EXPECT_FALSE(union_find.are_connected(i, j));
+        }
+    }
+}
+
+TEST(UnionFindDense, SingleComponentViaStarUnion)
+{
+    UnionFindDense<int> union_find(10);
+    const std::vector<int> set1{0, 2, 4, 6, 8};
+
+    // initially different sets are disconnected
+    for (size_t j = 0; j + 1 < set1.size(); ++j)
+        for (size_t i = j + 1; i < set1.size(); ++i)
+            EXPECT_FALSE(union_find.are_connected(set1[j], set1[i]));
+
+    UniteAll(union_find, set1);
+    // all connected
+    for (size_t j = 0; j < set1.size(); ++j)
+        for (size_t i = 0; i < set1.size(); ++i)
+            EXPECT_TRUE(union_find.are_connected(set1[j], set1[i]));
+}
+
+TEST(UnionFindDense, TwoComponentsThenMerged)
+{
+    UnionFindDense<int> union_find(10);
+    std::vector<int> set1{0, 2, 4, 6, 8};
+    std::vector<int> set2{1, 3, 5, 7, 9};
+
+    UniteAll(union_find, set1);
+    UniteAll(union_find, set2);
+
+    // Across components: not connected
+    for (int a : set1)
+        for (int b : set2)
+            EXPECT_FALSE(union_find.are_connected(a, b));
+
+    union_find.union_set(2, 3); // merge the two components
+
+    for (int a : set1)
+        for (int b : set2)
+            EXPECT_TRUE(union_find.are_connected(a, b));
+}
+
+TEST(UnionFindDense, FindRootValidAndInvalid)
+{
+    UnionFindDense<int> union_find(5);
+
+    for (int i = 0; i < 5; ++i)
+    {
+        auto r = union_find.find_root(i);
+        EXPECT_TRUE(r.has_value());
+        EXPECT_EQ(*r, i);
+    }
+
+    EXPECT_FALSE(union_find.find_root(-1).has_value());
+    EXPECT_FALSE(union_find.find_root(5).has_value());
+    EXPECT_FALSE(union_find.find_root(100).has_value());
+}
+
+TEST(UnionFindDense, InvalidInputsAreConnectedFalseUnionNoOp)
+{
+    UnionFindDense<int> union_find(3);
+
+    // are_connected should be false if any input invalid
+    EXPECT_FALSE(union_find.are_connected(-1, 0));
+    EXPECT_FALSE(union_find.are_connected(0, 3));
+    EXPECT_FALSE(union_find.are_connected(-1, 3));
+
+    // union_set should not crash and should not affect valid connectivity
+    union_find.union_set(-1, 0);
+    union_find.union_set(0, 3);
+    union_find.union_set(-1, 3);
+
+    EXPECT_FALSE(union_find.are_connected(0, 1));
+    EXPECT_FALSE(union_find.are_connected(1, 2));
+}
+
+TEST(UnionFindDense, UnionIsIdempotentAndSelfUnionSafe)
+{
+    UnionFindDense<int> union_find(4);
+
+    union_find.union_set(1, 2);
+    EXPECT_TRUE(union_find.are_connected(1, 2));
+
+    // repeat / reverse should not change correctness
+    union_find.union_set(1, 2);
+    union_find.union_set(2, 1);
+    EXPECT_TRUE(union_find.are_connected(1, 2));
+
+    // self union: should not break anything
+    union_find.union_set(2, 2);
+    EXPECT_TRUE(union_find.are_connected(1, 2));
+    EXPECT_FALSE(union_find.are_connected(0, 1));
+}
+
+TEST(UnionFindDense, TransitiveConnectivity)
+{
+    UnionFindDense<int> union_find(6);
+
+    union_find.union_set(0, 1);
+    union_find.union_set(1, 2);
+    union_find.union_set(2, 3);
 
+    EXPECT_TRUE(union_find.are_connected(0, 3));
+    EXPECT_TRUE(union_find.are_connected(1, 3));
+    EXPECT_FALSE(union_find.are_connected(0, 4));
+    EXPECT_FALSE(union_find.are_connected(3, 5));
+}