diff --git a/import-maps/common/README.md b/import-maps/common/README.md
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+# Import maps test JSON format
+
+In this directory, test inputs and expectations are expressed as JSON files.
+This is in order to share the same JSON files between WPT tests and Jest-based
+tests for the reference JavaScript implementation at [WICG repository](https://github.com/WICG/import-maps/tree/master/reference-implementation).
+
+## Basics
+
+A **test object** describes a set of parameters (import maps and base URLs) and specifiers to be tested.
+Each JSON file under [resources/](resources/) directory consists of a test object.
+A minimum test object would be:
+
+```json
+{
+ "name": "Main test name",
+ "importMapBaseURL": "https://example.com/import-map-base-url/index.html",
+ "importMap": {
+ "imports": {
+ "a": "/mapped-a.mjs"
+ }
+ },
+ "baseURL": "https://example.com/base-url/app.mjs",
+ "expectedResults": {
+ "a": "https://example.com/mapped-a.mjs",
+ "b": null
+ }
+}
+```
+
+Required fields:
+
+- `name`: Test name.
+ - In WPT tests, this is used for the test name of `promise_test()` together with specifier to be resolved, like `"Main test name: a"`.
+- `importMap` (object or string): the import map to be attached.
+- `importMapBaseURL` (string): the base URL used for [parsing the import map](https://wicg.github.io/import-maps/#parse-an-import-map-string).
+- `baseURL` (string): the base URL used in [resolving a specifier](https://wicg.github.io/import-maps/#resolve-a-module-specifier) for each specifiers.
+- `expectedResults` (object; string to (string or null)): test cases.
+ - The keys are specifiers to be resolved.
+ - The values are expected resolved URLs. If `null`, resolution should fail.
+
+Optional fields:
+
+- `link` and `details` can be used for e.g. linking to specs or adding more detailed descriptions.
+ - Currently they are simply ignored by the WPT test helper.
+
+## Nesting and inheritance
+
+We can organize tests by nesting test objects.
+A test object can contain child test objects (*subtests*) using `tests` field.
+The Keys of the `tests` value are the names of subtests, and values are test objects.
+
+For example:
+
+```json
+{
+ "name": "Main test name",
+ "importMapBaseURL": "https://example.com/import-map-base-url/index.html",
+ "importMap": {
+ "imports": {
+ "a": "/mapped-a.mjs"
+ }
+ },
+ "tests": {
+ "Subtest1": {
+ "baseURL": "https://example.com/base-url1/app.mjs",
+ "expectedResults": { "a": "https://example.com/mapped-a.mjs" }
+ },
+ "Subtest2": {
+ "baseURL": "https://example.com/base-url2/app.mjs",
+ "expectedResults": { "b": null }
+ }
+ }
+}
+```
+
+The top-level test object contains two sub test objects, named as `Subtest1` and `Subtest2`, respectively.
+
+Child test objects inherit fields from their parent test object.
+In the example above, the child test objects specifies `baseURL` fields, while they inherits other fields (e.g. `importMapBaseURL`) from the top-level test object.
diff --git a/import-maps/common/resolving.tentative.html b/import-maps/common/resolving.tentative.html
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+
+
+
+
+
+
diff --git a/import-maps/common/resources/common-test-helper.js b/import-maps/common/resources/common-test-helper.js
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+setup({allow_uncaught_exception : true});
+
+// Creates a new Document (via