terraform test: allow computed/mocked values override during planning (#36227)

Author: dsa0x

.changes/unreleased/ENHANCEMENTS-20250108-113433.yaml

@@ -0,0 +1,5 @@
+kind: ENHANCEMENTS
+body: '`terraform test`: Test runs now support using mocked or overridden values during unit test runs (e.g., with command = "plan"). When override_during = "plan"'
+time: 2025-01-08T11:34:33.709443+01:00
+custom:
+    Issue: "36227"

CHANGELOG.md

@@ -6,7 +6,6 @@ ENHANCEMENTS:
 
 * New command `modules -json`: Displays a full list of all installed modules in a working directory, including whether each module is currently referenced by the working directory's configuration. ([#35884](https://github.com/hashicorp/terraform/issues/35884))
 
-
 EXPERIMENTS:
 
 Experiments are only enabled in alpha releases of Terraform CLI. The following features are not yet available in stable releases.

internal/command/test_test.go

@@ -219,12 +219,25 @@ func TestTest_Runs(t *testing.T) {
 			code:        0,
 		},
 		"mocking": {
-			expectedOut: []string{"6 passed, 0 failed."},
+			expectedOut: []string{"9 passed, 0 failed."},
 			code:        0,
 		},
 		"mocking-invalid": {
-			expectedErr: []string{"Invalid outputs attribute"},
-			initCode:    1,
+			expectedErr: []string{
+				"Invalid outputs attribute",
+				"The override_during attribute must be a value of plan or apply.",
+			},
+			initCode: 1,
+		},
+		"mocking-error": {
+			expectedErr: []string{
+				"Unknown condition value",
+				"plan_mocked_overridden.tftest.hcl",
+				"test_resource.primary[0].id",
+				"plan_mocked_provider.tftest.hcl",
+				"test_resource.secondary[0].id",
+			},
+			code: 1,
 		},
 		"dangling_data_block": {
 			expectedOut: []string{"2 passed, 0 failed."},
@@ -1748,8 +1761,9 @@ Condition expression could not be evaluated at this time. This means you have
 executed a %s block with %s and one of the values your
 condition depended on is not known until after the plan has been applied.
 Either remove this value from your condition, or execute an %s command
-from this %s block.
-`, "`run`", "`command = plan`", "`apply`", "`run`"),
+from this %s block. Alternatively, if there is an override for this value,
+you can make it available during the plan phase by setting %s in the %s block.
+`, "`run`", "`command = plan`", "`apply`", "`run`", "`override_during =\nplan`", "`override_`"),
 		},
 		"unknown_value_in_vars": {
 			code: 1,

internal/command/testdata/test/mocking-error/child/main.tf

@@ -0,0 +1,30 @@
+terraform {
+  required_providers {
+    test = {
+      source = "hashicorp/test"
+      configuration_aliases = [test.primary, test.secondary]
+    }
+  }
+}
+
+variable "instances" {
+  type = number
+}
+
+resource "test_resource" "primary" {
+  provider = test.primary
+  count = var.instances
+}
+
+resource "test_resource" "secondary" {
+  provider = test.secondary
+  count = var.instances
+}
+
+output "primary" {
+  value = test_resource.primary
+}
+
+output "secondary" {
+  value = test_resource.secondary
+}

internal/command/testdata/test/mocking-error/main.tf

@@ -0,0 +1,46 @@
+terraform {
+  required_providers {
+    test = {
+      source = "hashicorp/test"
+    }
+  }
+}
+
+provider "test" {
+  alias = "primary"
+}
+
+provider "test" {
+  alias = "secondary"
+}
+
+variable "instances" {
+  type = number
+}
+
+variable "child_instances" {
+  type = number
+}
+
+resource "test_resource" "primary" {
+  provider = test.primary
+  count = var.instances
+}
+
+resource "test_resource" "secondary" {
+  provider = test.secondary
+  count = var.instances
+}
+
+module "child" {
+  count = var.instances
+
+  source = "./child"
+
+  providers = {
+    test.primary = test.primary
+    test.secondary = test.secondary
+  }
+
+  instances = var.child_instances
+}

internal/command/testdata/test/mocking-error/tests/plan_mocked_overridden.tftest.hcl

@@ -0,0 +1,34 @@
+mock_provider "test" {
+  alias = "primary"
+
+  mock_resource "test_resource" {
+    defaults = {
+      id = "aaaa"
+    }
+  }
+
+  override_resource {
+    target = test_resource.primary
+    values = {
+      id = "bbbb"
+    }
+  }
+}
+
+variables {
+  instances = 1
+  child_instances = 1
+}
+
+// This test will fail because the plan command does not use the
+// overridden values for computed properties, 
+// making the left-hand side of the condition unknown.
+run "test" {
+  command = plan
+
+  assert {
+    condition = test_resource.primary[0].id == "bbbb"
+    error_message = "plan should not have the overridden value"
+  }
+
+}

internal/command/testdata/test/mocking-error/tests/plan_mocked_provider.tftest.hcl

@@ -0,0 +1,25 @@
+mock_provider "test" {
+  alias = "secondary"
+
+  mock_resource "test_resource" {
+    defaults = {
+      id = "ffff"
+    }
+  }
+}
+
+
+variables {
+  instances = 2
+  child_instances = 1
+}
+
+run "test" {
+  command = plan
+
+  assert {
+    condition = test_resource.secondary[0].id == "ffff"
+    error_message = "plan should use the mocked provider value when override_during is plan"
+  }
+
+}

internal/command/testdata/test/mocking-invalid/tests/override_computed_invalid_boolean.tftest.hcl

@@ -0,0 +1,30 @@
+mock_provider "test" {
+  alias = "primary"
+  override_during = baz // This should either be plan or apply, therefore this test should fail
+
+  mock_resource "test_resource" {
+    defaults = {
+      id = "aaaa"
+    }
+  }
+
+  override_resource {
+    target = test_resource.primary
+    values = {
+      id = "bbbb"
+    }
+  }
+}
+
+variables {
+  instances = 1
+  child_instances = 1
+}
+
+run "test" {
+
+  assert {
+    condition = test_resource.primary[0].id == "bbbb"
+    error_message = "mock not applied"
+  }
+}

internal/command/testdata/test/mocking/tests/plan_mocked_overridden.tftest.hcl

@@ -0,0 +1,32 @@
+mock_provider "test" {
+  alias = "primary"
+
+  mock_resource "test_resource" {
+    defaults = {
+      id = "aaaa"
+    }
+  }
+
+  override_resource {
+    target = test_resource.primary
+    override_during = plan
+    values = {
+      id = "bbbb"
+    }
+  }
+}
+
+variables {
+  instances = 1
+  child_instances = 1
+}
+
+run "test" {
+  command = plan
+
+  assert {
+    condition = test_resource.primary[0].id == "bbbb"
+    error_message = "plan should override the value when override_during is plan"
+  }
+
+}

internal/command/testdata/test/mocking/tests/plan_mocked_provider.tftest.hcl

@@ -0,0 +1,26 @@
+mock_provider "test" {
+  alias = "secondary"
+  override_during = plan
+
+  mock_resource "test_resource" {
+    defaults = {
+      id = "ffff"
+    }
+  }
+}
+
+
+variables {
+  instances = 2
+  child_instances = 1
+}
+
+run "test" {
+  command = plan
+
+  assert {
+    condition = test_resource.secondary[0].id == "ffff"
+    error_message = "plan should use the mocked provider value when override_during is plan"
+  }
+
+}