More property tests

Also put proper comparison methods on `DerivedPath` and
`NixStringContextElem`, which is needed for the tests but good in
general.

src/libutil/tests/hash.cc

@@ -1,5 +1,12 @@
-#include "hash.hh"
+#include <regex>
+
+#include <nlohmann/json.hpp>
 #include <gtest/gtest.h>
+#include <rapidcheck/gtest.h>
+
+#include <hash.hh>
+
+#include "tests/hash.hh"
 
 namespace nix {
 
@@ -73,3 +80,16 @@ namespace nix {
                 "c7d329eeb6dd26545e96e55b874be909");
     }
 }
+
+namespace rc {
+using namespace nix;
+
+Gen<Hash> Arbitrary<Hash>::arbitrary()
+{
+    Hash hash(htSHA1);
+    for (size_t i = 0; i < hash.hashSize; ++i)
+        hash.hash[i] = *gen::arbitrary<uint8_t>();
+    return gen::just(hash);
+}
+
+}

src/libutil/tests/hash.hh

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <rapidcheck/gen/Arbitrary.h>
+
+#include <hash.hh>
+
+namespace rc {
+using namespace nix;
+
+template<>
+struct Arbitrary<Hash> {
+    static Gen<Hash> arbitrary();
+};
+
+}

src/libutil/tests/local.mk

@@ -2,7 +2,19 @@ check: libutil-tests_RUN
 
 programs += libutil-tests
 
-libutil-tests_NAME := libnixutil-tests
+libutil-tests-exe_NAME = libnixutil-tests
+
+libutil-tests-exe_DIR := $(d)
+
+libutil-tests-exe_INSTALL_DIR :=
+
+libutil-tests-exe_LIBS = libutil-tests
+
+libutil-tests-exe_LDFLAGS := $(GTEST_LIBS)
+
+libraries += libutil-tests
+
+libutil-tests_NAME = libnixutil-tests
 
 libutil-tests_DIR := $(d)
 
@@ -10,8 +22,8 @@ libutil-tests_INSTALL_DIR :=
 
 libutil-tests_SOURCES := $(wildcard $(d)/*.cc)
 
-libutil-tests_CXXFLAGS += -I src/libutil -I src/libexpr
+libutil-tests_CXXFLAGS += -I src/libutil
 
 libutil-tests_LIBS = libutil
 
-libutil-tests_LDFLAGS := $(GTEST_LIBS)
+libutil-tests_LDFLAGS := -lrapidcheck $(GTEST_LIBS)