uboot: (firmwareOdroidC2/C4) don't invoke patch tool, use patches = [] instead

https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh#L948
this can do it nicely.

Signed-off-by: Anton Arapov <anton@deadbeef.mx>

doc/builders/testers.chapter.md

@@ -0,0 +1,128 @@
+# Testers {#chap-testers}
+This chapter describes several testing builders which are available in the <literal>testers</literal> namespace.
+
+## `testVersion` {#tester-testVersion}
+
+Checks the command output contains the specified version
+
+Although simplistic, this test assures that the main program
+can run. While there's no substitute for a real test case,
+it does catch dynamic linking errors and such. It also provides
+some protection against accidentally building the wrong version,
+for example when using an 'old' hash in a fixed-output derivation.
+
+Examples:
+
+```nix
+passthru.tests.version = testVersion { package = hello; };
+
+passthru.tests.version = testVersion {
+  package = seaweedfs;
+  command = "weed version";
+};
+
+passthru.tests.version = testVersion {
+  package = key;
+  command = "KeY --help";
+  # Wrong '2.5' version in the code. Drop on next version.
+  version = "2.5";
+};
+```
+
+## `testEqualDerivation` {#tester-testEqualDerivation}
+
+Checks that two packages produce the exact same build instructions.
+
+This can be used to make sure that a certain difference of configuration,
+such as the presence of an overlay does not cause a cache miss.
+
+When the derivations are equal, the return value is an empty file.
+Otherwise, the build log explains the difference via `nix-diff`.
+
+Example:
+
+```nix
+testEqualDerivation
+  "The hello package must stay the same when enabling checks."
+  hello
+  (hello.overrideAttrs(o: { doCheck = true; }))
+```
+
+## `invalidateFetcherByDrvHash` {#tester-invalidateFetcherByDrvHash}
+
+Use the derivation hash to invalidate the output via name, for testing.
+
+Type: `(a@{ name, ... } -> Derivation) -> a -> Derivation`
+
+Normally, fixed output derivations can and should be cached by their output
+hash only, but for testing we want to re-fetch everytime the fetcher changes.
+
+Changes to the fetcher become apparent in the drvPath, which is a hash of
+how to fetch, rather than a fixed store path.
+By inserting this hash into the name, we can make sure to re-run the fetcher
+every time the fetcher changes.
+
+This relies on the assumption that Nix isn't clever enough to reuse its
+database of local store contents to optimize fetching.
+
+You might notice that the "salted" name derives from the normal invocation,
+not the final derivation. `invalidateFetcherByDrvHash` has to invoke the fetcher
+function twice: once to get a derivation hash, and again to produce the final
+fixed output derivation.
+
+Example:
+
+```nix
+tests.fetchgit = invalidateFetcherByDrvHash fetchgit {
+  name = "nix-source";
+  url = "https://github.com/NixOS/nix";
+  rev = "9d9dbe6ed05854e03811c361a3380e09183f4f4a";
+  sha256 = "sha256-7DszvbCNTjpzGRmpIVAWXk20P0/XTrWZ79KSOGLrUWY=";
+};
+```
+
+## `nixosTest` {#tester-nixosTest}
+
+Run a NixOS VM network test using this evaluation of Nixpkgs.
+
+NOTE: This function is primarily for external use. NixOS itself uses `make-test-python.nix` directly. Packages defined in Nixpkgs [reuse NixOS tests via `nixosTests`, plural](#ssec-nixos-tests-linking).
+
+It is mostly equivalent to the function `import ./make-test-python.nix` from the
+[NixOS manual](https://nixos.org/nixos/manual/index.html#sec-nixos-tests),
+except that the current application of Nixpkgs (`pkgs`) will be used, instead of
+letting NixOS invoke Nixpkgs anew.
+
+If a test machine needs to set NixOS options under `nixpkgs`, it must set only the
+`nixpkgs.pkgs` option.
+
+### Parameter
+
+A [NixOS VM test network](https://nixos.org/nixos/manual/index.html#sec-nixos-tests), or path to it. Example:
+
+```nix
+{
+  name = "my-test";
+  nodes = {
+    machine1 = { lib, pkgs, nodes, ... }: {
+      environment.systemPackages = [ pkgs.hello ];
+      services.foo.enable = true;
+    };
+    # machine2 = ...;
+  };
+  testScript = ''
+    start_all()
+    machine1.wait_for_unit("foo.service")
+    machine1.succeed("hello | foo-send")
+  '';
+}
+```
+
+### Result
+
+A derivation that runs the VM test.
+
+Notable attributes:
+
+ * `nodes`: the evaluated NixOS configurations. Useful for debugging and exploring the configuration.
+
+ * `driverInteractive`: a script that launches an interactive Python session in the context of the `testScript`.