Adding unittest for equation/pde/base.py (PaddlePaddle#397)

* Adding unittest for equation/pde/base.py

* Black code

* Changed the last unit test case

* pre-commit

* Adding more test for 100% coverage

* Black

test/equation/test_pde_base.py

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+import paddle
+import pytest
+import sympy
+from paddle import nn
+
+from ppsci.equation import PDE
+
+
+class Test_PDE:
+    def test_pde_init(self):
+        """
+        Testing the PDE class initialization
+        """
+        pde = PDE()
+        assert isinstance(pde, PDE)
+        assert isinstance(pde.equations, dict)
+        assert isinstance(pde.learnable_parameters, nn.ParameterList)
+
+    def test_pde_add_equation(self):
+        """
+        initiate a PDE object and add an equation to it
+        """
+        pde = PDE()
+
+        def simple_equation(out):
+            x, y = out["x"], out["y"]
+            return x + y
+
+        pde.add_equation("simple", simple_equation)
+
+        assert "simple" in pde.equations
+        assert pde.equations["simple"] == simple_equation
+        assert pde.equations["simple"]({"x": 1, "y": 2}) == 3
+
+        # redefine the equation and add again
+        def simple_equation2(out):
+            x, y = out["x"], out["y"]
+            return x - y
+
+        pde.add_equation("simple", simple_equation2)
+
+        assert pde.equations["simple"] == simple_equation2
+        assert pde.equations["simple"]({"x": 1, "y": 2}) == -1
+
+    def test_pde_create_symbols(self):
+        """
+        initiate a PDE object and add three symbols to it
+        """
+        pde = PDE()
+
+        # create symbols
+        x, y, z = pde.create_symbols("x y z")
+        assert isinstance(x, sympy.Symbol)
+        assert isinstance(y, sympy.Symbol)
+        assert isinstance(z, sympy.Symbol)
+
+    def test_pde_create_function(self):
+        """
+        initiate a PDE object and add a symbolic function to it
+        """
+        pde = PDE()
+
+        # create symbols
+        x, y, z = pde.create_symbols("x y z")
+
+        # create a function
+        f = pde.create_function(name="f", invars=(x, y, z))
+        assert isinstance(f, sympy.Function)
+        assert f.args == (x, y, z)
+
+    def test_pde_parameters(self):
+        """
+        initiate a PDE object and add a learnable parameter to it
+        """
+        pde = PDE()
+
+        assert len(pde.parameters()) == 0
+
+        # add a learnable parameter
+        pde.learnable_parameters.append(
+            paddle.create_parameter(shape=[1], dtype="float32")
+        )
+
+        assert len(pde.parameters()) == 1
+
+    def test_pde_state_dict(self):
+        """
+        initiate a PDE object, add a learnable parameter to it and check its state dict
+        """
+        pde = PDE()
+
+        assert len(pde.state_dict()) == 0
+
+        # add a learnable parameter
+        pde.learnable_parameters.append(
+            paddle.create_parameter(shape=[1], dtype="float32")
+        )
+
+        assert len(pde.state_dict()) == 1
+
+    def test_pde_set_state_dict(self):
+        """
+        initiate a PDE object, set its state dict and check its state dict
+        """
+        pde = PDE()
+
+        assert len(pde.state_dict()) == 0
+        # this is a paddle nn.ParameterList()
+        pde.learnable_parameters.append(
+            paddle.create_parameter(shape=[1], dtype="float32")
+        )
+        external_state = pde.state_dict()
+        # change the value in the external_state to 2
+        external_state["0"] = paddle.to_tensor([2.0])
+        pde.set_state_dict(external_state)
+        assert pde.state_dict()["0"] == paddle.to_tensor([2.0])
+
+    def test_str(self):
+        """
+        initiate a PDE object and check its string representation
+        """
+        pde = PDE()
+        assert str(pde) == "PDE"
+
+        # add an equation
+        def simple_equation(out):
+            x, y = out["x"], out["y"]
+            return x + y
+
+        pde.add_equation("simple", simple_equation)
+
+        assert str(pde).startswith("PDE, simple: ")
+
+
+if __name__ == "__main__":
+    pytest.main()