Implement initial spawn tests (just testing windowsEscape for now)

tests/unit/libutil/spawn.cc

@@ -0,0 +1,35 @@
+#include <gtest/gtest.h>
+
+#include "processes.hh"
+
+namespace nix {
+/*
+TEST(SpawnTest, spawnEcho)
+{
+auto output = runProgram(RunOptions{.program = "echo", .args = {}});
+}
+*/
+
+#ifdef _WIN32
+std::string windowsEscape(const std::string & str, bool cmd);
+
+TEST(SpawnTest, windowsEscape)
+{
+    auto empty = windowsEscape("", false);
+    ASSERT_EQ(empty, R"("")");
+    // There's no quotes in this argument so the input should equal the output
+    auto backslashStr = R"(\\\\)";
+    auto backslashes = windowsEscape(backslashStr, false);
+    ASSERT_EQ(backslashes, backslashStr);
+
+    auto nestedQuotes = windowsEscape(R"(he said: "hello there")", false);
+    ASSERT_EQ(nestedQuotes, R"("he said: \"hello there\"")");
+
+    auto middleQuote = windowsEscape(R"( \\\" )", false);
+    ASSERT_EQ(middleQuote, R"(" \\\\\\\" ")");
+
+    auto space = windowsEscape("hello world", false);
+    ASSERT_EQ(space, R"("hello world")");
+}
+#endif
+}