adding dhanibekov behavior test

Author: simon-lc

test/behaviors.jl

@@ -1,16 +1,16 @@
 @testset "Behavior: Quadruped simulation" begin
-    mech = get_mechanism(:quadruped, 
-        timestep=0.05, 
-        gravity=-9.81, 
-        friction_coefficient=0.8, 
-        damper=1000.0, 
+    mech = get_mechanism(:quadruped,
+        timestep=0.05,
+        gravity=-9.81,
+        friction_coefficient=0.8,
+        damper=1000.0,
         spring=30.0)
 
     initialize!(mech, :quadruped)
 
     try
-        storage = simulate!(mech, 5.0, 
-            record=true, 
+        storage = simulate!(mech, 5.0,
+            record=true,
             verbose=false)
         @test true
     catch
@@ -20,18 +20,18 @@ end
 
 @testset "Behavior: Box toss" begin
     for timestep in [0.10, 0.05, 0.01, 0.005]
-        mech = get_mechanism(:box, 
-            timestep=timestep, 
-            gravity=-9.81, 
+        mech = get_mechanism(:box,
+            timestep=timestep,
+            gravity=-9.81,
             friction_coefficient = 0.1)
 
-        initialize!(mech, :box, 
-            x=[0.0, 0.0, 0.5], 
-            v=[1.0, 1.5, 1.0], 
+        initialize!(mech, :box,
+            x=[0.0, 0.0, 0.5],
+            v=[1.0, 1.5, 1.0],
             ω=[5.0, 4.0, 2.0] .* timestep)
-        storage = simulate!(mech, 5.0, 
+        storage = simulate!(mech, 5.0,
             record=true,
-            opts=SolverOptions(btol=1e-6, rtol=1e-6, 
+            opts=SolverOptions(btol=1e-6, rtol=1e-6,
             verbose=false))
 
         @test norm(storage.v[1][end], Inf) < 1e-12
@@ -44,11 +44,11 @@ end
         # Mechanism
         timestep = 0.10
         mech = Dojo.get_fourbar(
-            model="fourbar", 
+            model="fourbar",
             timestep=timestep)
-        Dojo.initialize!(mech, :fourbar, 
-            angle=0.1, 
-            angular_velocity=[3.0, -3.0]) 
+        Dojo.initialize!(mech, :fourbar,
+            angle=0.1,
+            angular_velocity=[3.0, -3.0])
         loopjoints = mech.joints[end:end]
         Dojo.root_to_leaves_ordering(mech) == [2, 7, 3, 6, 1, 8, 4, 9]
 
@@ -65,3 +65,23 @@ end
         @test norm(min_coords[5] - (min_coords[2] - min_coords[1]), Inf) < 1.0e-5
     end
 end
+
+@testset "Behavior: Tennis Racket" begin
+    # Simulation
+    timestep=0.01
+    gravity=0.0
+    mech = get_mechanism(:dzhanibekov,
+            timestep=timestep,
+            gravity=gravity);
+
+    # Simulate
+    initialize_dzhanibekov!(mech,
+        angular_velocity=[15.0; 0.01; 0.0])
+    storage = simulate!(mech, 4.00,
+        record=true,
+        verbose=false)
+
+    # The x position of the side body oscillate between a positive and negative
+    # value when we observe the Dhanibekov effect. Otherwise, it always remains in the positive position.
+    @test minimum([x[1] for x in storage.x[2]]) < -0.05
+end