Working calculator

ServerTests/CalculatorTests.cs

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+using GrpcCalculator.Server;
+
+namespace GrpcCalculator.ServerTests;
+
+public class CalculatorTests
+{
+    [Fact]
+    public void SimpleAddition()
+    {
+        var calculator = new Calculator();
+        calculator = calculator.DigitPressed("5");
+        Assert.Equal("5", calculator.Display);
+        calculator = calculator.OperatorPressed(CalculatorOperator.Addition);
+        Assert.Equal("5", calculator.Display);
+        calculator = calculator.DigitPressed("4");
+        Assert.Equal("4", calculator.Display);
+        calculator = calculator.EqualsPressed();
+        Assert.Equal("9", calculator.Display);
+    }
+
+    [Fact]
+    public void JustEquals()
+    {
+        var calculator = new Calculator();
+        Assert.Equal("0", calculator.Display);
+        calculator = calculator.EqualsPressed();
+        Assert.Equal("0", calculator.Display);
+    }
+
+    [Fact]
+    public void MultipleEquals()
+    {
+        var calculator = new Calculator();
+        calculator = calculator.DigitPressed("2");
+        Assert.Equal("2", calculator.Display);
+        calculator = calculator.OperatorPressed(CalculatorOperator.Multiplication);
+        Assert.Equal("2", calculator.Display);
+        calculator = calculator.EqualsPressed();
+        Assert.Equal("4", calculator.Display);
+        calculator = calculator.EqualsPressed();
+        Assert.Equal("8", calculator.Display);
+    }
+}