feat: add platform_transition_test (#770)

* Add platform_transition_test

Signed-off-by: Thomas Lam <thomaslam@canva.com>

* Set target platform constraints for tests

Signed-off-by: Thomas Lam <thomaslam@canva.com>

* Update docs

Signed-off-by: Thomas Lam <thomaslam@canva.com>

---------

Signed-off-by: Thomas Lam <thomaslam@canva.com>

Author: lamcw

docs/transitions.md

@@ -1,7 +1,12 @@
 load("@bazel_skylib//rules:write_file.bzl", "write_file")
-load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library", "go_test")
 load("//lib:diff_test.bzl", "diff_test")
-load("//lib:transitions.bzl", "platform_transition_binary", "platform_transition_filegroup")
+load(
+    "//lib:transitions.bzl",
+    "platform_transition_binary",
+    "platform_transition_filegroup",
+    "platform_transition_test",
+)
 
 platform(
     name = "armv7_linux",
@@ -109,6 +114,11 @@ go_binary(
     visibility = ["//visibility:public"],
 )
 
+go_test(
+    name = "test_transition_test",
+    srcs = ["simple_test.go"],
+)
+
 platform_transition_binary(
     name = "transitioned_go_binary_x86_64",
     binary = ":test_transition_binary",
@@ -121,6 +131,26 @@ platform_transition_binary(
     target_platform = "arm64_linux",
 )
 
+platform_transition_test(
+    name = "transitioned_go_test_x86_64",
+    binary = ":test_transition_test",
+    # only run this test on x86_64 platforms
+    target_compatible_with = [
+        "@platforms//cpu:x86_64",
+    ],
+    target_platform = "x86_64_linux",
+)
+
+platform_transition_test(
+    name = "transitioned_go_test_arm64",
+    binary = ":test_transition_test",
+    # only run this test on arm64 platforms
+    target_compatible_with = [
+        "@platforms//cpu:arm64",
+    ],
+    target_platform = "arm64_linux",
+)
+
 sh_test(
     name = "test_go_binary_is_x86_64",
     srcs = ["test_file_type_contains.sh"],
@@ -141,6 +171,26 @@ sh_test(
     data = [":transitioned_go_binary_arm64"],
 )
 
+sh_test(
+    name = "test_go_test_is_x86_64",
+    srcs = ["test_file_type_contains.sh"],
+    args = [
+        "$(rootpath :transitioned_go_test_x86_64)",
+        "x86-64",
+    ],
+    data = [":transitioned_go_test_x86_64"],
+)
+
+sh_test(
+    name = "test_go_test_is_arm64",
+    srcs = ["test_file_type_contains.sh"],
+    args = [
+        "$(rootpath :transitioned_go_test_arm64)",
+        "aarch64",
+    ],
+    data = [":transitioned_go_test_arm64"],
+)
+
 go_library(
     name = "transitions_lib",
     srcs = ["main.go"],

lib/tests/transitions/BUILD.bazel

@@ -0,0 +1,10 @@
+package simple_test
+
+import "testing"
+
+func TestAdd(t *testing.T) {
+	result := 1 + 2
+	if result != 3 {
+		t.Errorf("got %q, wanted %q", result, 3)
+	}
+}

lib/tests/transitions/simple_test.go

@@ -87,19 +87,28 @@ def _platform_transition_binary_impl(ctx):
 
     return result
 
+_platform_transition_attrs = {
+    "basename": attr.string(),
+    "binary": attr.label(allow_files = True, cfg = _transition_platform),
+    "target_platform": attr.label(
+        doc = "The target platform to transition the binary.",
+        mandatory = True,
+    ),
+    "_allowlist_function_transition": attr.label(
+        default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
+    ),
+}
+
 platform_transition_binary = rule(
     implementation = _platform_transition_binary_impl,
-    attrs = {
-        "basename": attr.string(),
-        "binary": attr.label(allow_files = True, cfg = _transition_platform),
-        "target_platform": attr.label(
-            doc = "The target platform to transition the binary.",
-            mandatory = True,
-        ),
-        "_allowlist_function_transition": attr.label(
-            default = "@bazel_tools//tools/allowlists/function_transition_allowlist",
-        ),
-    },
+    attrs = _platform_transition_attrs,
     executable = True,
     doc = "Transitions the binary to use the provided platform.",
 )
+
+platform_transition_test = rule(
+    implementation = _platform_transition_binary_impl,
+    attrs = _platform_transition_attrs,
+    test = True,
+    doc = "Transitions the test to use the provided platform.",
+)