add center tests

tests/unit_tests/center.test.js

@@ -0,0 +1,52 @@
+describe('igraph.js', () => {
+  it('empty center', async () => {
+    const igraph = global.igraph;
+
+    const g = igraph.empty(0, false);
+
+    const center = igraph.graph_center(g, igraph.neimode.OUT);
+    expect(center.data).toEqual(new Int32Array([]));
+
+    center.delete();
+    g.delete();
+  });
+
+  it('undirected path graph center', async () => {
+    const igraph = global.igraph;
+
+    const g = igraph.ring(5, false, 0, 0);
+
+    const center = igraph.graph_center(g, igraph.neimode.OUT);
+    expect(center.data).toEqual(new Int32Array([2]));
+
+    center.delete();
+    g.delete();
+  });
+
+  it('undirected graph center', async () => {
+    const igraph = global.igraph;
+
+    const v = new igraph.vector_int([0, 1, 1, 2, 0, 2, 3, 0, 4, 1, 2, 5]);
+
+    const g = igraph.create(v, 6, false);
+    v.delete();
+
+    const center = igraph.graph_center(g, igraph.neimode.OUT);
+    expect(center.data).toEqual(new Int32Array([0, 1, 2]));
+
+    center.delete();
+    g.delete();
+  });
+
+  it('in-star graph center', async () => {
+    const igraph = global.igraph;
+
+    const g = igraph.star(10, igraph.starmode.OUT, 0);
+
+    const center = igraph.graph_center(g, igraph.neimode.OUT);
+    expect(center.data).toEqual(new Int32Array([1, 2, 3, 4, 5, 6, 7, 8, 9]));
+
+    center.delete();
+    g.delete();
+  });
+});