Add Unit Testing article

source/docs/software/wpilib-tools/robot-simulation/index.rst

@@ -8,3 +8,4 @@ Robot Simulation
    introduction
    simulation-gui
    physics-sim
+   unit-testing

source/docs/software/wpilib-tools/robot-simulation/unit-testing.rst

@@ -0,0 +1,204 @@
+Unit Testing
+============
+
+Unit testing is a method of testing code by dividing the code into the smallest "units" possible and testing each unit. In robot code, this can mean testing the code for each subsystem individually. There are many unit testing frameworks for most languages. Java robot projects have `JUnit 4 <https://junit.org/junit4/>`__ available by default, and C++ robot projects have `Google Test <https://github.com/google/googletest/blob/master/docs/primer.md>`__.
+
+Writing Testable Code
+^^^^^^^^^^^^^^^^^^^^^
+
+Our subsystem will be an Infinite Recharge intake mechanism containing a piston and a motor: the piston deploys/retracts the intake, and the motor will pull the Power Cells inside. Since it won't do anything, we don't want the motor to run if the intake mechanism isn't deployed.
+
+To provide a "clean slate" for each test, we need to have a function to destroy the object and free all hardware allocations. In Java, this is done by implementing the ``AutoCloseable`` interface and its ``.close()`` method, destroying each member object by calling its ``.close()`` method - an object without a ``.close()`` method probably doesn't need to be closed. In C++, the default destructor will be called automatically when the object goes out of scope and will call destructors of member objects.
+
+.. note:: This example can be easily adapted to the command-based paradigm by having ``Intake`` inherit from ``SubsystemBase``.
+
+.. tabs::
+   .. code-tab:: java
+
+      import edu.wpi.first.wpilibj.DoubleSolenoid;
+      import edu.wpi.first.wpilibj.PWMSparkMax;
+      import frc.robot.Constants.IntakeConstants;
+
+      public class Intake implements AutoCloseable {
+        private PWMSparkMax motor;
+        private DoubleSolenoid piston;
+
+        public Intake() {
+          motor = new PWMSparkMax(IntakeConstants.MOTOR_PORT);
+          piston = new DoubleSolenoid(IntakeConstants.PISTON_FWD, IntakeConstants.PISTON_REV);
+        }
+
+        public void deploy() {
+          piston.set(DoubleSolenoid.Value.kForward);
+        }
+
+        public void retract() {
+          piston.set(DoubleSolenoid.Value.kReverse);
+          motor.set(0); // turn off the motor
+        }
+
+        public void activate(double speed) {
+          if (piston.get() == DoubleSolenoid.Value.kForward) {
+            motor.set(speed);
+          } else { // if piston isn't open, do nothing
+            motor.set(0);
+          }
+        }
+
+        public void close() throws Exception {
+          piston.close();
+          motor.close();
+        }
+      }
+
+   .. group-tab:: C++ (Source)
+      .. code-block:: cpp
+
+      #include <frc2/command/SubsystemBase.h>
+      #include <frc/DoubleSolenoid.h>
+      #include <frc/PWMSparkMax.h>
+
+      #include "Constants.h"
+
+      class Intake : public frc2::SubsystemBase {
+       public:
+        Intake();
+        ~Intake();
+
+        void Deploy();
+        void Retract();
+        void Activate(double speed);
+
+       private:
+        frc::PWMSparkMax motor{Constants::Intake::MOTOR_PORT};
+        frc::DoubleSolenoid piston{Constants::Intake::PISTON_FWD, Constants::Intake::PISTON_REV};
+      };
+
+   .. group-tab:: C++ (Header)
+      .. code-block:: cpp
+
+      #include "subsystems/Intake.h"
+
+      Intake::Intake() = default;
+      Intake::~Intake() = default;
+
+      void Intake::Deploy() {
+          piston.Set(frc::DoubleSolenoid::Value::kForward);
+      }
+
+      void Intake::Retract() {
+          piston.Set(frc::DoubleSolenoid::Value::kReverse);
+          motor.Set(0);
+      }
+
+      void Intake::Activate(double speed) {
+          if (piston.Get() == frc::DoubleSolenoid::Value::kForward) {
+              motor.Set(speed);
+          } else { // if piston isn't open, do nothing
+              motor.Set(0);
+          }
+      }
+
+Writing Tests
+^^^^^^^^^^^^^
+
+Tests are placed inside the ``test`` source set: ``/src/test/java/`` and ``/src/test/native/`` for Java and C++ tests, respectively. Each test class contains at least one test method marked with ``@org.junit.Test``, each method represents a test case. Additional methods for opening resources (such as our ``Intake`` object) before each test and closing them after are respectively marked with ``@org.junit.Before`` and ``@org.junit.After``.
+
+Each test method should contain at least one *assertion* (``assert*()``/``EXPECT_*()``). These assertions verify a condition at runtime and fail the test if the condition isn't met. If there is more than one assertion in a test method, the first failed assertion will crash the test - execution won't reach the later assertions.
+
+Both JUnit and GoogleTest have multiple assertion types, but the most common is equality: ``assertEquals(expected, actual)``/``EXPECT_EQ(expected, actual)``. When comparing numbers, a third parameter - ``delta``, the acceptable error, can be given. In JUnit (Java), these assertions are static methods and can be used without qualification by adding the static star import ``import static org.junit.Asssert.*``. In Google Test (C++), assertions are macros from the ``<gtest/gtest.h>`` header.
+
+.. note:: Comparison of floating-point values isn't accurate, so comparing them should be done with an acceptable error parameter (``DELTA``).
+
+.. tabs::
+   .. code-tab:: java
+
+      import static org.junit.Assert.*;
+
+      import edu.wpi.first.hal.HAL;
+      import edu.wpi.first.wpilibj.simulation.PCMSim;
+      import edu.wpi.first.wpilibj.simulation.PWMSim;
+      import frc.robot.Constants.IntakeConstants;
+      import org.junit.*;
+
+      public class IntakeTest {
+        public static final double DELTA = 1e-2; // acceptable difference
+        Intake intake;
+        PWMSim simMotor;
+        PCMSim simPCM;
+
+        @Before // this method will run before each test
+        public void setup() {
+          assert HAL.initialize(500, 0); // initialize the HAL, crash if failed
+          intake = new Intake(); // create our intake
+          simMotor = new PWMSim(IntakeConstants.MOTOR_PORT); // create our simulation PWM
+          simPCM = new PCMSim(); // default PCM
+        }
+
+        @After // this method will run after each test
+        public void shutdown() throws Exception {
+          intake.close(); // destroy our intake object
+        }
+
+        @Test // marks this method as a test
+        public void doesntWorkWhenClosed() {
+          intake.retract(); // close the intake
+          intake.activate(0.5); // try to activate the motor
+          assertEquals(0.0, simMotor.getSpeed(), DELTA); // make sure that the value set to the motor is 0
+        }
+
+        @Test
+        public void worksWhenOpen() {
+          intake.deploy();
+          intake.activate(0.5);
+          assertEquals(0.5, simMotor.getSpeed(), DELTA);
+        }
+      }
+
+   .. code-tab:: cpp
+
+      #include <gtest/gtest.h>
+
+      #include <frc/simulation/PWMSim.h>
+      #include <frc/simulation/PCMSim.h>
+
+      #include "subsystems/Intake.h"
+      #include "Constants.h"
+
+      constexpr double DELTA = 1e-2;
+
+      class IntakeTest : public testing::Test {
+       protected:
+        Intake intake;
+        frc::sim::PWMSim simMotor{Constants::Intake::MOTOR_PORT};
+        frc::sim::PCMSim simPCM;
+      };
+
+      TEST_F(IntakeTest, DoesntWorkWhenClosed) {
+        intake.Retract(); // close the intake
+        intake.Activate(0.5); // try to activate the motor
+        EXPECT_EQ(0.0, simMotor.GetSpeed(), DELTA); // make sure that the value set to the motor is 0
+      }
+
+      TEST_F(IntakeTest, WorksWhenOpen) {
+        intake.Deploy();
+        intake.Activate(0.5);
+        EXPECT_EQ(0.5, simMotor.GetSpeed(), DELTA);
+      }
+
+For more advanced usage of JUnit and Google Test, see the framework docs.
+
+Running Tests
+^^^^^^^^^^^^^
+
+For Java tests to run, make sure that your ``build.gradle`` file contains the following block:
+
+.. code-block:: groovy
+
+  test {
+     useJUnit()
+  }
+
+Use :guilabel:`Test Robot Code` from the Command Palette to run the tests. Results will be reported in the terminal output, each test will have a ``FAILED`` or ``PASSED``/``OK`` label after the test name in the output. JUnit (Java only) will generate a HTML document in ``build/reports/tests/test/index.html`` with a more detailed overview of the results; if there are failied test a link to render the document in your browser will be printed in the terminal output.
+
+By default, Gradle runs the tests whenever robot code is built, including deploys. This will increase deploy time, and failing tests will cause the build and deploy to fail. To prevent this from happening, you can use :guilabel:`Change Skip Tests On Deploy Setting` from the Command Palette to configure whether to run tests when deploying.