diff --git a/src/placing.js b/src/placing.js
index cca2f71..5e227a8 100644
--- a/src/placing.js
+++ b/src/placing.js
@@ -182,7 +182,7 @@ module.exports = (options) => {
       let link, src, dst;
 
       //check overlapping
-      const list = Object.values(nodes);
+      const list = Object.values(nodes).filter(n => n.x !== undefined);
       for (let n1 = 0; n1 < list.length - 1; n1++) {
         for (let n2 = n1 + 1; n2 < list.length; n2++) {
           if (list[n1].x === list[n2].x && list[n1].y === list[n2].y) {
@@ -224,7 +224,7 @@ module.exports = (options) => {
               break;
             case 'right':
               if (dst.x - src.x <= 0) {
-                if (self.debug) console.log(` ${link.from} -> ${link.to}: invalid dx; ${dst.x - src.x} <= 0`);
+                if (self.debug) console.log(` ${link.from} -> ${link.to}: invalid dx: ${dst.x - src.x} <= 0`);
                 return false;
               }
               break;
diff --git a/test/placing.test.js b/test/placing.test.js
index 22d92d1..e594c3c 100644
--- a/test/placing.test.js
+++ b/test/placing.test.js
@@ -244,4 +244,117 @@ describe('getPosition', () => {
     }, 'a', false);
     expect(res).toEqual(null);
   });
+});
+
+describe('isValid', () => {
+  test('no nodes', () => {
+    const res = placing({debug: true}).isValid({}, []);
+    expect(res).toBe(true);
+  });
+  test('no placed nodes', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {}, 'b': {}
+    }, [
+      {from: 'a', to: 'b'}
+    ]);
+    expect(res).toBe(true);
+  });
+  test('one nodes', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {}
+    }, [
+      {from: 'a', to: 'b'}
+    ]);
+    expect(res).toBe(true);
+  });
+  test('overlapping nodes', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: 0, y: 0}
+    }, []);
+    expect(res).toBe(false);
+  });
+  test('in between node', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: 2, y: 0}, 'c': {name: 'c', x: 1, y: 0}
+    }, [
+      {from: 'a', to: 'b'}
+    ]);
+    expect(res).toBe(false);
+  });
+  test('invalid right link', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: -2, y: 2}
+    }, [
+      {from: 'a', to: 'b', direction: 'right'}
+    ]);
+    expect(res).toBe(false);
+  });
+  test('invalid left link', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: 2, y: 2}
+    }, [
+      {from: 'a', to: 'b', direction: 'left'}
+    ]);
+    expect(res).toBe(false);
+  });
+  test('invalid up link', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: 2, y: 2}
+    }, [
+      {from: 'a', to: 'b', direction: 'up'}
+    ]);
+    expect(res).toBe(false);
+  });
+  test('invalid down link', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: 2, y: -2}
+    }, [
+      {from: 'a', to: 'b', direction: 'down'}
+    ]);
+    expect(res).toBe(false);
+  });
+  test('valid right link', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: 2, y: 2}
+    }, [
+      {from: 'a', to: 'b', direction: 'right'}
+    ]);
+    expect(res).toBe(true);
+  });
+  test('valid left link', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: -2, y: 2}
+    }, [
+      {from: 'a', to: 'b', direction: 'left'}
+    ]);
+    expect(res).toBe(true);
+  });
+  test('valid up link', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: 2, y: -2}
+    }, [
+      {from: 'a', to: 'b', direction: 'up'}
+    ]);
+    expect(res).toBe(true);
+  });
+  test('valid down link', () => {
+    const res = placing({debug: true}).isValid({
+      'a': {name: 'a', x: 0, y: 0}, 'b': {name: 'b', x: 2, y: 2}
+    }, [
+      {from: 'a', to: 'b', direction: 'down'}
+    ]);
+    expect(res).toBe(true);
+  });
+});
+
+test('no debug (coverage)', () => {
+  placing({'max-link-length': 2, 'expand': 'h', diagonals: false}).compute({
+    '1': {name: '1'}, '2': {name: '2'}, '3': {name: '3'}, '4': {name: '4'}, '5': {name: '5'}, '6': {name: '6'}
+  }, [
+    {from: '1', to: '2', direction: 'right'},
+    {from: '1', to: '3', direction: 'down'},
+    {from: '3', to: '4', direction: 'right'},
+    {from: '4', to: '5', direction: 'up'},
+    {from: '3', to: '6', direction: 'left'}
+  ]);
 });
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