test: added tests for graph/kahn.go

Author: soondubu137

graph/kahn_test.go

@@ -0,0 +1,115 @@
+package graph
+
+import (
+	"testing"
+)
+
+func TestKahn(t *testing.T) {
+	testCases := []struct {
+		name         string
+		n            int
+		dependencies [][]int
+		wantNil      bool
+	}{
+		{
+			"linear graph",
+			3,
+			[][]int{{0, 1}, {1, 2}},
+			false,
+		},
+		{
+			"diamond graph",
+			4,
+			[][]int{{0, 1}, {0, 2}, {1, 3}, {2, 3}},
+			false,
+		},
+		{
+			"star graph",
+			5,
+			[][]int{{0, 1}, {0, 2}, {0, 3}, {0, 4}},
+			false,
+		},
+		{
+			"disconnected graph",
+			5,
+			[][]int{{0, 1}, {0, 2}, {3, 4}},
+			false,
+		},
+		{
+			"cycle graph 1",
+			4,
+			[][]int{{0, 1}, {1, 2}, {2, 3}, {3, 0}},
+			true,
+		},
+		{
+			"cycle graph 2",
+			4,
+			[][]int{{0, 1}, {1, 2}, {2, 0}, {2, 3}},
+			true,
+		},
+		{
+			"single node graph",
+			1,
+			[][]int{},
+			false,
+		},
+		{
+			"empty graph",
+			0,
+			[][]int{},
+			false,
+		},
+		{
+			"redundant dependencies",
+			4,
+			[][]int{{0, 1}, {1, 2}, {1, 2}, {2, 3}},
+			false,
+		},
+		{
+			"island vertex",
+			4,
+			[][]int{{0, 1}, {0, 2}},
+			false,
+		},
+		{
+			"more complicated graph",
+			14,
+			[][]int{{1, 9}, {2, 0}, {3, 2}, {4, 5}, {4, 6}, {4, 7}, {6, 7},
+				{7, 8}, {9, 4}, {10, 0}, {10, 1}, {10, 12}, {11, 13},
+				{12, 0}, {12, 11}, {13, 5}},
+			false,
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			actual := Kahn(tc.n, tc.dependencies)
+			if tc.wantNil {
+				if actual != nil {
+					t.Errorf("Kahn(%d, %v) = %v; want nil", tc.n, tc.dependencies, actual)
+				}
+			} else {
+				if actual == nil {
+					t.Errorf("Kahn(%d, %v) = nil; want valid order", tc.n, tc.dependencies)
+				} else {
+					seen := make([]bool, tc.n)
+					positions := make([]int, tc.n)
+					for i, v := range actual {
+						seen[v] = true
+						positions[v] = i
+					}
+					for i, v := range seen {
+						if !v {
+							t.Errorf("missing vertex %v", i)
+						}
+					}
+					for _, d := range tc.dependencies {
+						if positions[d[0]] > positions[d[1]] {
+							t.Errorf("dependency %v not satisfied", d)
+						}
+					}
+				}
+			}
+		})
+	}
+}