Support passing in variables into tests (#91)

* Support passing variables into tests

* Add test for test variables

* PR Feedback

internal/go/skycfg/skycfg_test.go

@@ -45,10 +45,16 @@ def test_helper1(t):
 	x = helper1()
 	t.assert(x == 12345)
 
+def test_main(ctx):
+	msg = main(ctx)[0]
+	ctx.assert(len(msg.r_string) == 1)
+	ctx.assert(msg.r_string[0] == "var_value")
+
 def main(ctx):
 	msg = test_proto.MessageV2()
 	msg.f_int64 = helper1()
 	msg.f_string = json.encode(helper2(ctx))
+	msg.r_string.append(ctx.vars["var_key"])
 
 	return [msg]
 `,
@@ -275,6 +281,7 @@ func TestSkycfgEndToEnd(t *testing.T) {
 					FString: proto.String(
 						`{"key1":"value1","key2":"key3=value3","key4":{"key5":"value5","var_key":"var_value"}}`,
 					),
+					RString: []string{"var_value"},
 				},
 			},
 		},
@@ -380,11 +387,6 @@ func TestSkycfgTesting(t *testing.T) {
 		t.Error("Unexpected error loading test1.sky", err)
 	}
 
-	tests := config.Tests()
-	if len(tests) != 4 {
-		t.Error("Expected 4 tests but found", len(tests))
-	}
-
 	cases := map[string]testTestCase{
 		"test_helper1": testTestCase{
 			passes: true,
@@ -399,10 +401,20 @@ func TestSkycfgTesting(t *testing.T) {
 		"test_helper2_errors": testTestCase{
 			errors: true,
 		},
+		"test_main": testTestCase{
+			passes: true,
+		},
+	}
+
+	tests := config.Tests()
+	if len(tests) != len(cases) {
+		t.Error("Expected %d tests but found %d", len(cases), len(tests))
 	}
 
 	for _, test := range tests {
-		result, err := test.Run(ctx)
+		result, err := test.Run(ctx, skycfg.WithTestVars(starlark.StringDict{
+			"var_key": starlark.String("var_value"),
+		}))
 		testCase, ok := cases[test.Name()]
 		if !ok {
 			t.Error("Could not find test case for test", test.Name())

skycfg.go

@@ -436,9 +436,39 @@ func (t *Test) Name() string {
 	return t.callable.Name()
 }
 
+// An TestOption adjusts details of how a Skycfg config's test functions are
+// executed.
+type TestOption interface {
+	applyTest(*testOptions)
+}
+
+type testOptions struct {
+	vars *starlark.Dict
+}
+
+type fnTestOption func(*testOptions)
+
+func (fn fnTestOption) applyTest(opts *testOptions) { fn(opts) }
+
+// WithTestVars adds key:value pairs to the ctx.vars dict passed to tests
+func WithTestVars(vars starlark.StringDict) TestOption {
+	return fnTestOption(func(opts *testOptions) {
+		for key, value := range vars {
+			opts.vars.SetKey(starlark.String(key), value)
+		}
+	})
+}
+
 // Run actually executes a test. It returns a TestResult if the test completes (even if it fails)
 // The error return value will only be non-nil if the test execution itself errors.
-func (t *Test) Run(ctx context.Context) (*TestResult, error) {
+func (t *Test) Run(ctx context.Context, opts ...TestOption) (*TestResult, error) {
+	parsedOpts := &testOptions{
+		vars: &starlark.Dict{},
+	}
+	for _, opt := range opts {
+		opt.applyTest(parsedOpts)
+	}
+
 	thread := &starlark.Thread{
 		Print: skyPrint,
 	}
@@ -448,7 +478,7 @@ func (t *Test) Run(ctx context.Context) (*TestResult, error) {
 	testCtx := &impl.Module{
 		Name: "skycfg_test_ctx",
 		Attrs: starlark.StringDict(map[string]starlark.Value{
-			"vars":   &starlark.Dict{},
+			"vars":   parsedOpts.vars,
 			"assert": assertModule,
 		}),
 	}