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Add observable scan tests #44481

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207 changes: 207 additions & 0 deletions dom/observable/tentative/observable-scan.any.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,207 @@
test(() => {
const source = new Observable((subscriber) => {
subscriber.next(1);
subscriber.next(2);
subscriber.next(3);
subscriber.complete();
});

const reducerCalls = 0;
const reducerArgs = [];
const results = [];

source
.scan((acc, value, index) => {
reducerCalls++;
reducerArgs.push(acc, value, index);
return acc + value;
}, 0)
.subscribe({
next: (value) => results.push(value),
error: (e) => results.push(e.message),
complete: () => results.push("complete"),
});

assert_equals(
reducerCalls,
3,
"observable scan should call the reducer once for each value emitted by the source observable"
);
assert_array_equals(
reducerArgs,
[0, 1, 0, 1, 2, 1, 3, 3, 2],
"observable scan should call the reducer with the current state, the current value, and the current index"
);
assert_array_equals(
results,
[1, 3, 6, "complete"],
"observable scan should reduce and emit state changes by processing values from the source observable, mirroring completion"
);
}, "observable scan should reduce and emit state changes by processing values from the source observable, mirroring completion");

test(() => {
const source = new Observable((subscriber) => {
subscriber.next(1);
subscriber.next(2);
subscriber.next(3);
subscriber.error(new Error("error from source"));
});

const reducerCalls = 0;
const reducerArgs = [];
const results = [];

source
.scan((acc, value, index) => {
reducerCalls++;
reducerArgs.push(acc, value, index);
return acc + value;
}, 0)
.subscribe({
next: (value) => results.push(value),
error: (e) => results.push(e.message),
complete: () => results.push("complete"),
});

assert_equals(
reducerCalls,
3,
"observable scan should call the reducer once for each value emitted by the source observable"
);
assert_array_equals(
reducerArgs,
[0, 1, 0, 1, 2, 1, 3, 3, 2],
"observable scan should call the reducer with the current state, the current value, and the current index"
);
assert_array_equals(
results,
[1, 3, 6, "error from source"],
"observable scan should reduce and emit state changes by processing values from the source observable, mirroring errors"
);
}, "observable scan should reduce and emit state changes by processing values from the source observable, mirroring errors");

test(() => {
const source = new Observable((subscriber) => {
subscriber.next(1);
subscriber.next(2);
subscriber.next(3);
subscriber.complete();
});

const reducerCalls = 0;
const reducerArgs = [];
const results = [];

source
.scan((acc, value, index) => {
reducerCalls++;
reducerArgs.push(acc, value, index);
return acc + value;
})
.subscribe({
next: (value) => results.push(value),
error: (e) => results.push(e.message),
complete: () => results.push("complete"),
});

assert_equals(
reducerCalls,
2,
"observable scan should call the reducer once for each value emitted by the source observable"
);
assert_array_equals(
reducerArgs,
[1, 2, 1, 3, 3, 2],
"observable scan should call the reducer with the current state, the current value, and the current index"
);
assert_array_equals(
results,
[1, 3, 6, "complete"],
"observable scan should reduce and emit state changes by processing values from the source observable, mirroring completion"
);
}, "if no initial state is provided, scan should use and emit the first value from the source observable as the initial state");

test(() => {
const source = new Observable((subscriber) => {
subscriber.next(1);
subscriber.next(2);
subscriber.next(3);
});

const results = [];

source
.scan((acc, value) => {
if (value === 2) {
throw new Error("error while reducing");
}
return acc + value;
}, 0)
.subscribe({
next: () => results.push("next"),
error: (e) => results.push(e.message),
complete: () => results.push("complete"),
});

assert_array_equals(
results,
[1, "error while reducing"],
"if an error is thrown in the reducer, it should be caught and sent to the error callback"
);
}, "if an error is thrown in the reducer, it should be caught and sent to the error callback");

test(() => {
let teardownCalls = 0;
const source = new Observable((subscriber) => {
subscriber.addTeardown(() => {
teardownCalls++;
});
});

const controller = new AbortController();

source
.scan(() => 0)
.subscribe(
{},
{
signal: controller.signal,
}
);

assert_equals(
teardownCalls,
0,
"unsubscribing from the result of scan should unsubscribe from the source observable"
);

controller.abort();

assert_equals(
teardownCalls,
1,
"unsubscribing from the result of scan should unsubscribe from the source observable"
);
}, "unsubscribing from the result of scan should unsubscribe from the source observable");

test(() => {
const source = new Observable((subscriber) => {
subscriber.error(new Error("error from source"));
});

const results = [];

source
.scan(() => 0)
.subscribe({
next: () => results.push("next"),
error: (e) => results.push(e.message),
complete: () => results.push("complete"),
});

assert_array_equals(
results,
["error from source"],
"errors from the source observable are passed through to the result observable"
);
}, "if no initial state is provided, and the source observable errors before it emits a value, the result should forward the error");