Confusing output for width and depth from resource estimator

src/Simulation/Simulators.Tests/Circuits/ResourcesEstimator.qs

@@ -16,4 +16,24 @@ namespace Microsoft.Quantum.Simulation.Simulators.Tests
             ResetAll([q[1], q[0]]);
         }
     }
+
+    // Tests for Depth and Width lower bounds
+    operation DepthDifferentQubits () : Unit
+    {
+        using(q = Qubit[3]) {
+            T(q[0]);
+            T(q[1]);
+            T(q[2]);
+            T(q[0]);
+        }
+    }
+    operation DepthVersusWidth () : Unit
+    {
+        using(q = Qubit()) {
+            T(q);
+        }
+        using(q = Qubit()) {
+            T(q);
+        }
+    }
 }

src/Simulation/Simulators.Tests/ResourcesEstimatorTests.cs

@@ -100,6 +100,43 @@ public void ToTSVTest()
             var cliffords = rows.First(r => r.StartsWith("QubitClifford")).Split('\t');
             Assert.Equal(2, cliffords.Length);
             Assert.Equal("2", cliffords[1]);
+        }
+
+        /// <summary>
+        /// Shows that T gates on different qubits are counted for depth purposes as 
+        /// executing in parallel.
+        /// </summary>
+        [Fact]
+        public void DepthDifferentQubitsTest()
+        {
+            var sim = new ResourcesEstimator();
+
+            // using(q = Qubit[3]) { T(q[0]); T(q[1]); T(q[3]); T(q[0]); }
+            DepthDifferentQubits.Run(sim).Wait();
+            var data = sim.Data;
+
+            Assert.Equal(4.0, data.Rows.Find("T")["Sum"]);
+            Assert.Equal(3.0, data.Rows.Find("Width")["Sum"]);
+            Assert.Equal(2.0, data.Rows.Find("Depth")["Sum"]);
+        }
+
+        /// <summary>
+        /// Documents that the width and depth statistics reflect independent lower
+        /// bounds for each (two T gates cannot be combined into a circuit of depth
+        /// one and width one).
+        /// </summary>
+        [Fact]
+        public void DepthVersusWidthTest()
+        {
+            var sim = new ResourcesEstimator();
+
+            // using(q = Qubit()) { T(q); } using(q = Qubit()) { T(q); } (yes, twice)
+            DepthVersusWidth.Run(sim).Wait();
+            var data = sim.Data;
+
+            Assert.Equal(2.0, data.Rows.Find("T")["Sum"]);
+            Assert.Equal(1.0, data.Rows.Find("Width")["Sum"]);
+            Assert.Equal(1.0, data.Rows.Find("Depth")["Sum"]);
         }
     }
 }