diff --git a/terraform/eval.go b/terraform/eval.go
index 7a274d14cc..54cbbeba24 100644
--- a/terraform/eval.go
+++ b/terraform/eval.go
@@ -19,8 +19,10 @@ type EvalNode interface {
 	// and not used at runtime.
 	Args() ([]EvalNode, []EvalType)
 
-	// Eval evaluates this node with the given context.
-	Eval(EvalContext) (interface{}, error)
+	// Eval evaluates this node with the given context. The second parameter
+	// are the argument values. These will match in order and 1-1 with the
+	// results of the Args() return value.
+	Eval(EvalContext, []interface{}) (interface{}, error)
 
 	// Type returns the type that will be returned by this node.
 	Type() EvalType
@@ -31,3 +33,28 @@ type EvalNode interface {
 type GraphNodeEvalable interface {
 	EvalTree() EvalNode
 }
+
+// MockEvalContext is a mock version of EvalContext that can be used
+// for tests.
+type MockEvalContext struct {
+	InitProviderCalled   bool
+	InitProviderName     string
+	InitProviderProvider ResourceProvider
+	InitProviderError    error
+
+	ProviderCalled   bool
+	ProviderName     string
+	ProviderProvider ResourceProvider
+}
+
+func (c *MockEvalContext) InitProvider(n string) (ResourceProvider, error) {
+	c.InitProviderCalled = true
+	c.InitProviderName = n
+	return c.InitProviderProvider, c.InitProviderError
+}
+
+func (c *MockEvalContext) Provider(n string) ResourceProvider {
+	c.ProviderCalled = true
+	c.ProviderName = n
+	return c.ProviderProvider
+}
diff --git a/terraform/eval_interpolate.go b/terraform/eval_interpolate.go
index ea7846b966..a0ef21cb0a 100644
--- a/terraform/eval_interpolate.go
+++ b/terraform/eval_interpolate.go
@@ -14,7 +14,8 @@ func (n *EvalInterpolate) Args() ([]EvalNode, []EvalType) {
 	return nil, nil
 }
 
-func (n *EvalInterpolate) Eval(ctx EvalContext) (interface{}, error) {
+func (n *EvalInterpolate) Eval(
+	ctx EvalContext, args []interface{}) (interface{}, error) {
 	return nil, nil
 }
 
diff --git a/terraform/eval_literal.go b/terraform/eval_literal.go
new file mode 100644
index 0000000000..2159298721
--- /dev/null
+++ b/terraform/eval_literal.go
@@ -0,0 +1,20 @@
+package terraform
+
+// EvalLiteral is an EvalNode implementation that returns a literal
+// value. This is very useful for testing as well as in practice.
+type EvalLiteral struct {
+	Value     interface{}
+	ValueType EvalType
+}
+
+func (n *EvalLiteral) Args() ([]EvalNode, []EvalType) {
+	return nil, nil
+}
+
+func (n *EvalLiteral) Eval(EvalContext, []interface{}) (interface{}, error) {
+	return n.Value, nil
+}
+
+func (n *EvalLiteral) Type() EvalType {
+	return n.ValueType
+}
diff --git a/terraform/eval_literal_test.go b/terraform/eval_literal_test.go
new file mode 100644
index 0000000000..f82a5613d1
--- /dev/null
+++ b/terraform/eval_literal_test.go
@@ -0,0 +1,27 @@
+package terraform
+
+import (
+	"testing"
+)
+
+func TestEvalLiteral_impl(t *testing.T) {
+	var _ EvalNode = new(EvalLiteral)
+}
+
+func TestEvalLiteralEval(t *testing.T) {
+	n := &EvalLiteral{Value: 42}
+	actual, err := n.Eval(nil, nil)
+	if err != nil {
+		t.Fatalf("err: %s", err)
+	}
+	if actual != 42 {
+		t.Fatalf("bad: %#v", actual)
+	}
+}
+
+func TestEvalLiteralType(t *testing.T) {
+	n := &EvalLiteral{Value: 42, ValueType: EvalTypeConfig}
+	if actual := n.Type(); actual != EvalTypeConfig {
+		t.Fatalf("bad: %#v", actual)
+	}
+}
diff --git a/terraform/eval_provider.go b/terraform/eval_provider.go
index f2c9115bf9..032515da68 100644
--- a/terraform/eval_provider.go
+++ b/terraform/eval_provider.go
@@ -16,7 +16,8 @@ func (n *EvalConfigProvider) Args() ([]EvalNode, []EvalType) {
 		[]EvalType{EvalTypeResourceProvider, EvalTypeConfig}
 }
 
-func (n *EvalConfigProvider) Eval(ctx EvalContext) (interface{}, error) {
+func (n *EvalConfigProvider) Eval(
+	ctx EvalContext, args []interface{}) (interface{}, error) {
 	return nil, nil
 }
 
@@ -35,7 +36,8 @@ func (n *EvalInitProvider) Args() ([]EvalNode, []EvalType) {
 	return nil, nil
 }
 
-func (n *EvalInitProvider) Eval(ctx EvalContext) (interface{}, error) {
+func (n *EvalInitProvider) Eval(
+	ctx EvalContext, args []interface{}) (interface{}, error) {
 	return ctx.InitProvider(n.Name)
 }
 
@@ -53,7 +55,8 @@ func (n *EvalGetProvider) Args() ([]EvalNode, []EvalType) {
 	return nil, nil
 }
 
-func (n *EvalGetProvider) Eval(ctx EvalContext) (interface{}, error) {
+func (n *EvalGetProvider) Eval(
+	ctx EvalContext, args []interface{}) (interface{}, error) {
 	result := ctx.Provider(n.Name)
 	if result == nil {
 		return nil, fmt.Errorf("provider %s not initialized", n.Name)
diff --git a/terraform/eval_provider_test.go b/terraform/eval_provider_test.go
new file mode 100644
index 0000000000..ba56dc22db
--- /dev/null
+++ b/terraform/eval_provider_test.go
@@ -0,0 +1,49 @@
+package terraform
+
+import (
+	"testing"
+)
+
+func TestEvalInitProvider_impl(t *testing.T) {
+	var _ EvalNode = new(EvalInitProvider)
+}
+
+func TestEvalInitProvider(t *testing.T) {
+	n := &EvalInitProvider{Name: "foo"}
+	provider := &MockResourceProvider{}
+	ctx := &MockEvalContext{InitProviderProvider: provider}
+	if actual, err := n.Eval(ctx, nil); err != nil {
+		t.Fatalf("err: %s", err)
+	} else if actual != provider {
+		t.Fatalf("bad: %#v", actual)
+	}
+
+	if !ctx.InitProviderCalled {
+		t.Fatal("should be called")
+	}
+	if ctx.InitProviderName != "foo" {
+		t.Fatalf("bad: %#v", ctx.InitProviderName)
+	}
+}
+
+func TestEvalGetProvider_impl(t *testing.T) {
+	var _ EvalNode = new(EvalGetProvider)
+}
+
+func TestEvalGetProvider(t *testing.T) {
+	n := &EvalGetProvider{Name: "foo"}
+	provider := &MockResourceProvider{}
+	ctx := &MockEvalContext{ProviderProvider: provider}
+	if actual, err := n.Eval(ctx, nil); err != nil {
+		t.Fatalf("err: %s", err)
+	} else if actual != provider {
+		t.Fatalf("bad: %#v", actual)
+	}
+
+	if !ctx.ProviderCalled {
+		t.Fatal("should be called")
+	}
+	if ctx.ProviderName != "foo" {
+		t.Fatalf("bad: %#v", ctx.ProviderName)
+	}
+}
diff --git a/terraform/eval_test.go b/terraform/eval_test.go
new file mode 100644
index 0000000000..e89f2641bf
--- /dev/null
+++ b/terraform/eval_test.go
@@ -0,0 +1,9 @@
+package terraform
+
+import (
+	"testing"
+)
+
+func TestMockEvalContext_impl(t *testing.T) {
+	var _ EvalContext = new(MockEvalContext)
+}