Don't run libstore unit tests in project root

This keeps the libstore unit tests from writing
`libstore-unit-tests.xml` to the project root.

Change-Id: I0d9909aabf9f3574cc1e72a5ae81daefba9a394b

tests/unit/libstore-support/tests/test-data.hh

@@ -0,0 +1,25 @@
+#pragma once
+
+#include "util.hh"
+#include "types.hh"
+
+namespace nix {
+
+// TODO: These helpers should be available in all unit tests.
+
+/**
+ * The path to the unit test data directory. See the contributing guide
+ * in the manual for further details.
+ */
+static Path getUnitTestData() {
+    return getEnv("_NIX_TEST_UNIT_DATA").value();
+}
+
+/**
+ * Resolve a path under the unit test data directory to an absolute path.
+ */
+static Path getUnitTestDataPath(std::string_view path) {
+    return absPath(getUnitTestData() + "/" + path);
+}
+
+}

tests/unit/libstore/machines.cc

@@ -1,5 +1,6 @@
 #include "machines.hh"
 #include "globals.hh"
+#include "tests/test-data.hh"
 
 #include <gmock/gmock-matchers.h>
 
@@ -17,7 +18,6 @@ using nix::getMachines;
 using nix::Machine;
 using nix::Machines;
 using nix::pathExists;
-using nix::Settings;
 using nix::settings;
 
 class Environment : public ::testing::Environment {
@@ -138,7 +138,7 @@ TEST(machines, getMachinesWithIncorrectFormat) {
 }
 
 TEST(machines, getMachinesWithCorrectFileReference) {
-    auto path = absPath("tests/unit/libstore/test-data/machines.valid");
+    auto path = nix::getUnitTestDataPath("machines.valid");
     ASSERT_TRUE(pathExists(path));
 
     settings.builders = std::string("@") + path;
@@ -165,6 +165,6 @@ TEST(machines, getMachinesWithIncorrectFileReference) {
 }
 
 TEST(machines, getMachinesWithCorrectFileReferenceToIncorrectFile) {
-    settings.builders = std::string("@") + absPath("tests/unit/libstore/test-data/machines.bad_format");
+    settings.builders = std::string("@") + nix::getUnitTestDataPath("machines.bad_format");
     EXPECT_THROW(getMachines(), FormatError);
 }

tests/unit/meson.build

@@ -85,6 +85,7 @@ libstore_test_support_sources = files(
   'libstore-support/tests/derived-path.cc',
   'libstore-support/tests/outputs-spec.cc',
   'libstore-support/tests/path.cc',
+  'libstore-support/tests/test-data.hh',
 )
 
 libstore_test_support = library(
@@ -142,7 +143,6 @@ test(
     '_NIX_TEST_UNIT_DATA': meson.project_source_root() / 'tests/unit/libstore/data',
   },
   suite : 'check',
-  workdir : meson.project_source_root(),
   protocol : 'gtest',
   verbose : true,
 )