cpp-either-stream/test/either_stream_test.cxx

//
//  either_stream.t.h
//  optional.stream
//
//  Created by Sam Jaffe on 1/30/17.
//

#pragma once

#include <cxxtest/TestSuite.h>

#include "either_stream.hpp"

enum class MathError {
  OutOfBounds,
  DivideByZero,
  DomainError
};

using MathObject = either<double, MathError>;

MathObject divide(double num, double den) {
  if (std::abs(den) < 0.000000001) {
    return MathError::DivideByZero;
  } else {
    return num / den;
  }
}

double multiply(double lhs, double rhs) { return lhs * rhs; }

MathObject log(double value, double base) {
  if (value <= 0) {
    return MathError::DomainError;
  } else {
    return divide(std::log(value), std::log(base));
  }
}

class either_stream_TestSuite : public CxxTest::TestSuite {
public:
  void test_either_becomes_error() {
    auto strm = stream::either::make_stream<MathObject>(1.0);
    strm.flatmap([](double d) { return divide(d, 0); })
    .match([](double) { TS_FAIL("Expected Error Type"); },
           [](MathError e) { TS_ASSERT_EQUALS( MathError::DivideByZero, e ); });
  }
  
  void test_either_computes_result() {
    auto strm = stream::either::make_stream<MathObject>(1.0);
    strm.map([](double d) { return multiply(d, 10.0); })
    .match([](double d) { TS_ASSERT_DELTA(10.0, d, 0.00001); },
           [](MathError) { TS_FAIL("Expected Value"); });
  }
  
  void test_either_computes_result2() {
    auto strm = stream::either::make_stream<MathObject>(1.0);
    bool is_error = strm.map([](double d) { return multiply(d, 10.0); })
    .match([](double) { return false; },
           [](MathError) { return true; });
    TS_ASSERT(!is_error);
  }
  
  void test_either_propogates_error() {
    auto strm = stream::either::make_stream<MathObject>(1.0);
    strm.flatmap([](double d) { return divide(d, 0); })
    .map([](double) { TS_FAIL("Operating on bad data"); return 0; })
    .match([](double) { TS_FAIL("Expected Error Type"); },
           [](MathError e) { TS_ASSERT_EQUALS( MathError::DivideByZero, e ); });
  }
  
  void test_either_propogates_same_error() {
    auto strm = stream::either::make_stream<MathObject>(1.0);
    strm.flatmap([](double d) { return log(1.0, d); })
    .flatmap([](double d) { return log(d, 1.0); })
    .match([](double) { TS_FAIL("Expected Error Type"); },
           [](MathError e) { TS_ASSERT_EQUALS( MathError::DivideByZero, e ); });
  }

  void test_either_propogates_same_error2() {
    auto strm = stream::either::make_stream<MathObject>(1.0);
    strm.flatmap([](double d) { return log(0.0, d); })
    .flatmap([](double d) { return log(d, 1.0); })
    .match([](double) { TS_FAIL("Expected Error Type"); },
           [](MathError e) { TS_ASSERT_EQUALS( MathError::DomainError, e ); });
  }
  
  void test_either_propogates_same_error3() {
    auto strm = stream::either::make_stream<MathObject>(1.0);
    bool is_error = strm.flatmap([](double d) { return log(0.0, d); })
    .flatmap([](double d) { return log(d, 1.0); })
    .match([](double) { return false; },
           [](MathError) { return true; });
    TS_ASSERT(is_error);
  }

};