diff --git a/internal/states/resource_test.go b/internal/states/resource_test.go
index 53447e3d40f0..221e41abb0ae 100644
--- a/internal/states/resource_test.go
+++ b/internal/states/resource_test.go
@@ -8,6 +8,15 @@ import (
 )
 
 func TestResourceInstanceDeposeCurrentObject(t *testing.T) {
+	t.Run("nil resource", func(t *testing.T) {
+		var nilRI *ResourceInstance
+		dk := nilRI.deposeCurrentObject(NotDeposed)
+		t.Logf("deposedKey (nil receiver) is %q", dk)
+
+		if dk != NotDeposed {
+			t.Fatalf("expected NotDeposed for nil receiver, got %q", dk)
+		}
+	})
 	obj := &ResourceInstanceObjectSrc{
 		// Empty for the sake of this test, because we're just going to
 		// compare by pointer below anyway.
diff --git a/internal/states/state_test.go b/internal/states/state_test.go
index 5dc36e4b0b01..0ce3f74c806d 100644
--- a/internal/states/state_test.go
+++ b/internal/states/state_test.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"reflect"
 	"testing"
+	"time"
 
 	"github.com/go-test/deep"
 	"github.com/google/go-cmp/cmp"
@@ -337,6 +338,18 @@ func TestStateHasResourceInstanceObjects(t *testing.T) {
 				s := ss.Lock()
 				delete(s.Modules[""].Resources["test.foo"].Instances, addrs.NoKey)
 				ss.Unlock()
+				done := make(chan struct{})
+				go func() {
+					ss.Lock()
+					ss.Unlock()
+					close(done)
+				}()
+				select {
+				case <-done:
+					// OK: lock was released
+				case <-time.After(500 * time.Millisecond):
+					t.Fatalf("Unlock did not release SyncState lock (timed out acquiring lock again)")
+				}
 			},
 			false,
 		},
@@ -1009,6 +1022,70 @@ func TestState_MoveModule(t *testing.T) {
 	})
 }
 
+func TestState_ProviderAddrs(t *testing.T) {
+	// 1) nil state
+	var nilState *State
+	if got := nilState.ProviderAddrs(); got != nil {
+		t.Fatalf("nil state: expected nil, got %#v", got)
+	}
+
+	// 2) empty state
+	empty := NewState()
+	if got := empty.ProviderAddrs(); got != nil {
+		t.Fatalf("empty state: expected nil, got %#v", got)
+	}
+
+	// 3) populated state
+	s := NewState()
+
+	rootAWS := addrs.AbsProviderConfig{
+		Module:   addrs.RootModule,
+		Provider: addrs.NewDefaultProvider("aws"),
+	}
+	rootGoogle := addrs.AbsProviderConfig{
+		Module:   addrs.RootModule,
+		Provider: addrs.NewDefaultProvider("google"),
+	}
+	childAWS := addrs.AbsProviderConfig{
+		Module:   addrs.RootModule.Child("child"),
+		Provider: addrs.NewDefaultProvider("aws"),
+	}
+
+	rm := s.RootModule()
+	rm.SetResourceInstanceCurrent(
+		addrs.Resource{Mode: addrs.ManagedResourceMode, Type: "test_thing", Name: "foo"}.Instance(addrs.NoKey),
+		&ResourceInstanceObjectSrc{Status: ObjectReady, SchemaVersion: 1, AttrsJSON: []byte(`{}`)},
+		rootAWS,
+	)
+
+	rm.SetResourceInstanceCurrent(
+		addrs.Resource{Mode: addrs.ManagedResourceMode, Type: "test_thing", Name: "bar"}.Instance(addrs.NoKey),
+		&ResourceInstanceObjectSrc{Status: ObjectReady, SchemaVersion: 1, AttrsJSON: []byte(`{}`)},
+		rootAWS,
+	)
+
+	rm.SetResourceInstanceCurrent(
+		addrs.Resource{Mode: addrs.ManagedResourceMode, Type: "test_thing", Name: "baz"}.Instance(addrs.NoKey),
+		&ResourceInstanceObjectSrc{Status: ObjectReady, SchemaVersion: 1, AttrsJSON: []byte(`{}`)},
+		rootGoogle,
+	)
+
+	childMI := addrs.RootModuleInstance.Child("child", addrs.NoKey)
+	cm := s.EnsureModule(childMI)
+	cm.SetResourceInstanceCurrent(
+		addrs.Resource{Mode: addrs.ManagedResourceMode, Type: "test_thing", Name: "child"}.Instance(addrs.NoKey),
+		&ResourceInstanceObjectSrc{Status: ObjectReady, SchemaVersion: 1, AttrsJSON: []byte(`{}`)},
+		childAWS,
+	)
+
+	got := s.ProviderAddrs()
+	expected := []addrs.AbsProviderConfig{childAWS, rootAWS, rootGoogle}
+
+	if !reflect.DeepEqual(got, expected) {
+		t.Fatalf("unexpected provider addrs\nexpected: %#v\ngot: %#v", expected, got)
+	}
+}
+
 func mustParseModuleInstanceStr(str string) addrs.ModuleInstance {
 	addr, diags := addrs.ParseModuleInstanceStr(str)
 	if diags.HasErrors() {