Move unit tests to the location Meson expects them to be

Everything that is a separate subproject should live in the subprojects
directory.

Progress on #2503

This reverts commit 451f8a8c19.

src/libstore-tests/http-binary-cache-store.cc

@@ -0,0 +1,21 @@
+#include <gtest/gtest.h>
+
+#include "http-binary-cache-store.hh"
+
+namespace nix {
+
+TEST(HttpBinaryCacheStore, constructConfig)
+{
+    HttpBinaryCacheStoreConfig config{"http", "foo.bar.baz", {}};
+
+    EXPECT_EQ(config.cacheUri, "http://foo.bar.baz");
+}
+
+TEST(HttpBinaryCacheStore, constructConfigNoTrailingSlash)
+{
+    HttpBinaryCacheStoreConfig config{"https", "foo.bar.baz/a/b/", {}};
+
+    EXPECT_EQ(config.cacheUri, "https://foo.bar.baz/a/b");
+}
+
+} // namespace nix