diff --git a/.github/workflows/terraform-test.yaml b/.github/workflows/terraform-test.yaml
index 7e3c49d..09d328f 100644
--- a/.github/workflows/terraform-test.yaml
+++ b/.github/workflows/terraform-test.yaml
@@ -51,3 +51,7 @@ jobs:
         run: terraform -chdir=terraform init -backend=false
       - name: Terraform test
         run: terraform -chdir=terraform test
+      - name: Terraform init repository module
+        run: terraform -chdir=terraform/modules/repository init -backend=false
+      - name: Terraform test repository module
+        run: terraform -chdir=terraform/modules/repository test
diff --git a/README.md b/README.md
index d266bf0..1827107 100644
--- a/README.md
+++ b/README.md
@@ -201,7 +201,7 @@ terraform -chdir=terraform apply
 
 Format Terraform configuration by `terraform -chdir=terraform fmt -recursive`.
 
-Test by `terraform -chdir=terraform init -backend=false && terraform -chdir=terraform test`.
+Test by `terraform -chdir=terraform init -backend=false && terraform -chdir=terraform test`, the repository module by `terraform -chdir=terraform/modules/repository init -backend=false && terraform -chdir=terraform/modules/repository test`.
 
 ## Copyright and Licensing
 
diff --git a/terraform/modules/repository/tests/repository.tftest.hcl b/terraform/modules/repository/tests/repository.tftest.hcl
new file mode 100644
index 0000000..53490bb
--- /dev/null
+++ b/terraform/modules/repository/tests/repository.tftest.hcl
@@ -0,0 +1,483 @@
+mock_provider "github" {}
+
+run "name_only" {
+  command = plan
+
+  variables {
+    repository = {
+      name = "foo"
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.name == "foo"
+    error_message = "Unexpected name."
+  }
+
+  assert {
+    condition     = github_repository.this.description == null && github_repository.this.homepage_url == null && github_repository.this.is_template == null
+    error_message = "Unset optional attributes must be null."
+  }
+
+  assert {
+    condition     = length(github_repository.this.template) == 0
+    error_message = "Unexpected template block."
+  }
+
+  assert {
+    condition     = github_repository.this.archive_on_destroy
+    error_message = "Repository must archive on destroy."
+  }
+
+  assert {
+    condition     = github_repository.this.delete_branch_on_merge
+    error_message = "Repository must delete branches on merge."
+  }
+}
+
+run "name_leading_dot" {
+  command = plan
+
+  variables {
+    repository = {
+      name = ".github"
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.name == ".github"
+    error_message = "Unexpected name."
+  }
+}
+
+run "name_max_length" {
+  command = plan
+
+  variables {
+    repository = {
+      name = "${join("", [for i in range(100) : "a"])}"
+    }
+  }
+
+  assert {
+    condition     = length(github_repository.this.name) == 100
+    error_message = "Unexpected name."
+  }
+}
+
+run "name_empty" {
+  command = plan
+
+  variables {
+    repository = {
+      name = ""
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "name_dot" {
+  command = plan
+
+  variables {
+    repository = {
+      name = "."
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "name_dot_dot" {
+  command = plan
+
+  variables {
+    repository = {
+      name = ".."
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "name_space" {
+  command = plan
+
+  variables {
+    repository = {
+      name = "foo bar"
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "name_slash" {
+  command = plan
+
+  variables {
+    repository = {
+      name = "foo/bar"
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "name_too_long" {
+  command = plan
+
+  variables {
+    repository = {
+      name = "${join("", [for i in range(101) : "a"])}"
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "description" {
+  command = plan
+
+  variables {
+    repository = {
+      name        = "foo"
+      description = "Foo bar."
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.description == "Foo bar."
+    error_message = "Unexpected description."
+  }
+}
+
+run "homepage_url_https" {
+  command = plan
+
+  variables {
+    repository = {
+      name         = "foo"
+      homepage_url = "https://example.com"
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.homepage_url == "https://example.com"
+    error_message = "Unexpected homepage_url."
+  }
+}
+
+run "homepage_url_http" {
+  command = plan
+
+  variables {
+    repository = {
+      name         = "foo"
+      homepage_url = "http://example.com"
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.homepage_url == "http://example.com"
+    error_message = "Unexpected homepage_url."
+  }
+}
+
+run "homepage_url_empty" {
+  command = plan
+
+  variables {
+    repository = {
+      name         = "foo"
+      homepage_url = ""
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.homepage_url == ""
+    error_message = "Unexpected homepage_url."
+  }
+}
+
+run "homepage_url_no_scheme" {
+  command = plan
+
+  variables {
+    repository = {
+      name         = "foo"
+      homepage_url = "example.com"
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "homepage_url_ftp" {
+  command = plan
+
+  variables {
+    repository = {
+      name         = "foo"
+      homepage_url = "ftp://example.com"
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "topics" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = ["terraform", "github-organization", "c3po"]
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.topics == toset(["terraform", "github-organization", "c3po"])
+    error_message = "Unexpected topics."
+  }
+}
+
+run "topics_empty" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = []
+    }
+  }
+
+  assert {
+    condition     = length(github_repository.this.topics) == 0
+    error_message = "Unexpected topics."
+  }
+}
+
+run "topics_max" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = [for i in range(20) : "topic-${i}"]
+    }
+  }
+
+  assert {
+    condition     = length(github_repository.this.topics) == 20
+    error_message = "Unexpected topics."
+  }
+}
+
+run "topic_max_length" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = [join("", [for i in range(50) : "a"])]
+    }
+  }
+
+  assert {
+    condition     = length(github_repository.this.topics) == 1
+    error_message = "Unexpected topics."
+  }
+}
+
+run "topics_uppercase" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = ["Terraform"]
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "topics_leading_hyphen" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = ["-terraform"]
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "topics_underscore" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = ["terraform_github"]
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "topics_empty_string" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = [""]
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "topics_too_long" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = [join("", [for i in range(51) : "a"])]
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "topics_too_many" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = [for i in range(21) : "topic-${i}"]
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "topics_duplicate" {
+  command = plan
+
+  variables {
+    repository = {
+      name   = "foo"
+      topics = ["terraform", "iac", "terraform"]
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "is_template_true" {
+  command = plan
+
+  variables {
+    repository = {
+      name        = "foo"
+      is_template = true
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.is_template == true
+    error_message = "Unexpected is_template."
+  }
+}
+
+run "is_template_false" {
+  command = plan
+
+  variables {
+    repository = {
+      name        = "foo"
+      is_template = false
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.is_template == false
+    error_message = "Unexpected is_template."
+  }
+}
+
+run "template" {
+  command = plan
+
+  variables {
+    repository = {
+      name     = "foo"
+      template = { owner = "bruzit", repository = "template" }
+    }
+  }
+
+  assert {
+    condition     = length(github_repository.this.template) == 1
+    error_message = "Expected one template block."
+  }
+
+  assert {
+    condition     = github_repository.this.template[0].owner == "bruzit" && github_repository.this.template[0].repository == "template"
+    error_message = "Unexpected template."
+  }
+
+  assert {
+    condition     = !github_repository.this.template[0].include_all_branches
+    error_message = "include_all_branches must default to false."
+  }
+}
+
+run "template_include_all_branches" {
+  command = plan
+
+  variables {
+    repository = {
+      name     = "foo"
+      template = { owner = "bruzit", repository = "template", include_all_branches = true }
+    }
+  }
+
+  assert {
+    condition     = github_repository.this.template[0].include_all_branches
+    error_message = "Unexpected include_all_branches."
+  }
+}
+
+run "template_owner_empty" {
+  command = plan
+
+  variables {
+    repository = {
+      name     = "foo"
+      template = { owner = "", repository = "template" }
+    }
+  }
+
+  expect_failures = [var.repository]
+}
+
+run "template_repository_empty" {
+  command = plan
+
+  variables {
+    repository = {
+      name     = "foo"
+      template = { owner = "bruzit", repository = " " }
+    }
+  }
+
+  expect_failures = [var.repository]
+}
diff --git a/terraform/modules/repository/variables.tf b/terraform/modules/repository/variables.tf
index 0c7c86d..087fa6a 100644
--- a/terraform/modules/repository/variables.tf
+++ b/terraform/modules/repository/variables.tf
@@ -12,4 +12,28 @@ variable "repository" {
     }))
   })
   description = "Repository configuration"
+  validation {
+    condition     = try(can(regex("^[A-Za-z0-9._-]{1,100}$", var.repository.name)) && !contains([".", ".."], var.repository.name), false)
+    error_message = "Repository name \"${try(coalesce(var.repository.name), "")}\" must be 1-100 characters of A-Z, a-z, 0-9, ., -, _ other than \".\" and \"..\"."
+  }
+  validation {
+    condition     = try(var.repository.topics == null ? true : alltrue([for t in var.repository.topics : can(regex("^[a-z0-9][a-z0-9-]{0,49}$", t))]), false)
+    error_message = "Repository ${try(coalesce(var.repository.name), "")}: invalid topic(s) ${try(join(", ", [for t in var.repository.topics : "\"${t}\"" if !can(regex("^[a-z0-9][a-z0-9-]{0,49}$", t))]), "")}; each must be lowercase letters, digits, hyphens, start with a letter or digit, max 50 characters."
+  }
+  validation {
+    condition     = try(var.repository.topics == null ? true : length(var.repository.topics) <= 20, false)
+    error_message = "Repository ${try(coalesce(var.repository.name), "")}: at most 20 topics, got ${try(length(var.repository.topics), 0)}."
+  }
+  validation {
+    condition     = try(var.repository.topics == null ? true : length(distinct(var.repository.topics)) == length(var.repository.topics), false)
+    error_message = "Repository ${try(coalesce(var.repository.name), "")}: duplicate topic(s) ${try(join(", ", distinct([for i, t in var.repository.topics : t if contains(slice(var.repository.topics, 0, i), t)])), "")}."
+  }
+  validation {
+    condition     = try(var.repository.homepage_url == null || var.repository.homepage_url == "" ? true : startswith(var.repository.homepage_url, "http://") || startswith(var.repository.homepage_url, "https://"), false)
+    error_message = "Repository ${try(coalesce(var.repository.name), "")}: homepage_url \"${try(coalesce(var.repository.homepage_url), "")}\" must start with http:// or https://."
+  }
+  validation {
+    condition     = try(var.repository.template == null ? true : trimspace(var.repository.template.owner) != "" && trimspace(var.repository.template.repository) != "", false)
+    error_message = "Repository ${try(coalesce(var.repository.name), "")}: template owner and repository must be non-empty."
+  }
 }