Implement generic testing for 2019.

This method reads a specific directory and applies all inputs there to
their proper implementation.

2019/tests/samples/01-1-1.in

@@ -0,0 +1,4 @@
++1
+-2
++3
++1

2019/tests/samples/01-1-1.out

@@ -0,0 +1 @@
+3

2019/tests/samples/01-1-2.in

@@ -0,0 +1,3 @@
++1
++1
++1

2019/tests/samples/01-1-2.out

@@ -0,0 +1 @@
+3

2019/tests/samples/01-1-3.in

@@ -0,0 +1,3 @@
++1
++1
+-2

2019/tests/samples/01-1-3.out

@@ -0,0 +1 @@
+0

2019/tests/samples/01-1-4.in

@@ -0,0 +1,3 @@
+-1
+-2
+-3

2019/tests/samples/01-1-4.out

@@ -0,0 +1 @@
+-6

2019/tests/test_solutions.cpp

@@ -1,24 +1,53 @@
 #define BOOST_TEST_MODULE solutions_tests
 
+#include <filesystem>
+#include <regex>
 #include <string>
+#include <tuple>
 #include <boost/test/included/unit_test.hpp>
+#include <boost/test/data/test_case.hpp>
 #include "solutions.hpp"
 
-static std::string run_day1_part1(std::string_view input) {
-    std::stringstream input_stream;
-    input_stream.write(input.data(), input.size());
+std::vector<std::string> get_samples() {
+    std::vector<std::string> samples;
+    for (auto entry : std::filesystem::directory_iterator("./samples")) {
+        if (entry.path().filename().extension() == ".in") {
+            samples.push_back(entry.path().string());
+        }
+    }
 
-    std::stringstream output_stream;
-
-    aoc2019::day01_part1(input_stream, output_stream);
-    return output_stream.str();
+    return samples;
 }
 
-BOOST_AUTO_TEST_CASE(sample_day1_part1)
-{
-    BOOST_TEST(run_day1_part1("+1\n-2\n+3\n+1") == "3\n");
-    BOOST_TEST(run_day1_part1("+1\n+1\n+1") == "3\n");
-    BOOST_TEST(run_day1_part1("+1\n+1\n-2") == "0\n");
+static std::string read_file(const std::string &file_name) {
+    std::ifstream file(file_name);
+    return std::string(std::istreambuf_iterator<char>(file),
+                       std::istreambuf_iterator<char>());
 }
 
+static void test_solution_impl(const std::string &input_name) {
+    std::regex name_parser("/(\\d{2})-(1|2).*\\.in$");
+    std::smatch match;
+    // Sanity check, is this a parseable input file?
+    BOOST_TEST(std::regex_search(input_name, match, name_parser));
 
+    const auto output_filename = input_name.substr(0, input_name.length() - 3) + ".out";
+    const int day = std::atoi(match[1].str().c_str());
+    const int part2 = match[2].str() == "2";
+
+    const auto desired_output = read_file(output_filename);
+    const auto implementation = aoc2019::get_implementation(day, part2);
+
+    std::stringstream output_buffer;
+    std::ifstream input(input_name);
+
+    implementation(input, output_buffer);
+
+    BOOST_TEST(desired_output == output_buffer.str());
+}
+
+BOOST_DATA_TEST_CASE(test_solution,
+                     boost::unit_test::data::make(get_samples()),
+                     input_name) {
+    test_solution_impl(input_name);
+}