backend/local: Fix mock provider in tests

We've changed the contract for PlanResourceChange to now require the
provider to populate any default values (including unknowns) it wants to
set for computed arguments, so our mock provider here now needs to be a
little more complex to deal with that.

This fixes several of the tests in this package. A minor change to
TestLocal_applyEmptyDirDestroy was required to make it properly configure
the mock provider so PlanResourceChange can access the schema.

backend/local/backend_apply_test.go

@@ -123,8 +123,7 @@ func TestLocal_applyError(t *testing.T) {
 	b, cleanup := TestLocal(t)
 	defer cleanup()
 
-	p := TestLocalProvider(t, b, "test", nil)
-	p.GetSchemaReturn = &terraform.ProviderSchema{
+	schema := &terraform.ProviderSchema{
 		ResourceTypes: map[string]*configschema.Block{
 			"test_instance": {
 				Attributes: map[string]*configschema.Attribute{
@@ -134,6 +133,7 @@ func TestLocal_applyError(t *testing.T) {
 			},
 		},
 	}
+	p := TestLocalProvider(t, b, "test", schema)
 
 	var lock sync.Mutex
 	errored := false

backend/local/testing.go

@@ -6,7 +6,11 @@ import (
 	"path/filepath"
 	"testing"
 
+	"github.com/zclconf/go-cty/cty"
+
+	"github.com/hashicorp/terraform/addrs"
 	"github.com/hashicorp/terraform/backend"
+	"github.com/hashicorp/terraform/configs/configschema"
 	"github.com/hashicorp/terraform/providers"
 	"github.com/hashicorp/terraform/states"
 	"github.com/hashicorp/terraform/states/statemgr"
@@ -38,9 +42,14 @@ func TestLocal(t *testing.T) (*Local, func()) {
 			// function, t.Helper doesn't apply and so the log source
 			// isn't correctly shown in the test log output. This seems
 			// unavoidable as long as this is happening so indirectly.
-			t.Log(diag.Description().Summary)
+			desc := diag.Description()
+			if desc.Detail != "" {
+				t.Logf("%s: %s", desc.Summary, desc.Detail)
+			} else {
+				t.Log(desc.Summary)
+			}
 			if local.CLI != nil {
-				local.CLI.Error(diag.Description().Summary)
+				local.CLI.Error(desc.Summary)
 			}
 		}
 	}
@@ -59,10 +68,34 @@ func TestLocal(t *testing.T) (*Local, func()) {
 func TestLocalProvider(t *testing.T, b *Local, name string, schema *terraform.ProviderSchema) *terraform.MockProvider {
 	// Build a mock resource provider for in-memory operations
 	p := new(terraform.MockProvider)
+
+	if schema == nil {
+		schema = &terraform.ProviderSchema{} // default schema is empty
+	}
 	p.GetSchemaReturn = schema
+
 	p.PlanResourceChangeFn = func(req providers.PlanResourceChangeRequest) providers.PlanResourceChangeResponse {
+		rSchema, _ := schema.SchemaForResourceType(addrs.ManagedResourceMode, req.TypeName)
+		if rSchema == nil {
+			rSchema = &configschema.Block{} // default schema is empty
+		}
+		plannedVals := map[string]cty.Value{}
+		for name, attrS := range rSchema.Attributes {
+			val := req.ProposedNewState.GetAttr(name)
+			if attrS.Computed && val.IsNull() {
+				val = cty.UnknownVal(attrS.Type)
+			}
+			plannedVals[name] = val
+		}
+		for name := range rSchema.BlockTypes {
+			// For simplicity's sake we just copy the block attributes over
+			// verbatim, since this package's mock providers are all relatively
+			// simple -- we're testing the backend, not esoteric provider features.
+			plannedVals[name] = req.ProposedNewState.GetAttr(name)
+		}
+
 		return providers.PlanResourceChangeResponse{
-			PlannedState:   req.ProposedNewState,
+			PlannedState:   cty.ObjectVal(plannedVals),
 			PlannedPrivate: req.PriorPrivate,
 		}
 	}