STOCKHOLDERS AGREEMENT

Exhibit 10.1

STOCKHOLDERS’ AGREEMENT

This STOCKHOLDERS’ AGREEMENT (this “Agreement”), is dated as of September 1, 2008, by and between Teradyne, Inc., a Massachusetts corporation (“Parent”) and the stockholders listed on the signature pages hereto (each a “Stockholder” and collectively, the “Stockholders”).

W I T N E S S E T H:

WHEREAS, Parent, Turin Acquisition Corp., a Delaware corporation and a direct wholly owned subsidiary of Parent (“Merger Sub”), and Eagle Test Systems, Inc., a Delaware corporation (the “Company”), are entering into an Agreement and Plan of Merger, dated as of the date hereof (as it may be amended from time to time in accordance with its terms, the “Merger Agreement”), providing for, among other things, the merger of Merger Sub with and into the Company with the Company surviving the merger as a wholly owned subsidiary of Parent, in each case, on the terms and subject to the conditions set forth in therein (capitalized terms used herein and not otherwise defined shall have the meanings ascribed to such terms in the Merger Agreement); and

WHEREAS, as of the date hereof, each Stockholder is the record and beneficial owner of the number of shares of Common Stock set forth, and in the manner reflected, on Attachment A hereto (the “Owned Shares”); and

WHEREAS, as a condition to each of Parent and Merger Sub’s willingness to enter into and perform their respective obligations under the Merger Agreement, Parent and Merger Sub have required that each Stockholder agree, and each Stockholder has agreed, (i) to vote all of such Stockholder’s Owned Shares as well as any shares of Common Stock acquired by such Stockholder after the execution of this Agreement (all of which, after so acquired, shall constitute “Owned Shares”), whether upon the exercise of options, conversion of convertible securities or otherwise, and any other voting securities of the Company (whether acquired heretofore or hereafter) that are beneficially owned by such Stockholder or over which such Stockholder has, directly or indirectly, the right to vote (collectively, the “Voting Shares”) in favor of any proposal in furtherance of the Merger Agreement or the transactions contemplated thereby, including the Merger, and (ii) to take the other actions described herein; and

WHEREAS, each Stockholder desires to express its support for the Merger Agreement and the transactions contemplated thereby, including the Merger, by executing this Agreement; and

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration given to each party hereto, the receipt of which is hereby acknowledged, the parties agree as follows:

1. Agreement to Vote; Irrevocable Proxy.

1.1 Agreement to Vote. Each Stockholder hereby agrees that, during the time this Agreement is in effect, at any meeting of the stockholders of the Company, however called, or any adjournment or postponement thereof, such Stockholder shall be present (in person or by

proxy) and vote (or cause to be voted) all of its Voting Shares (a) in favor of the adoption of the Merger Agreement and (b) against any Alternative Proposal and against any action or agreement that would delay, prevent, impede or impair the ability of Parent and Merger Sub to complete the Merger or the ability of the Company to consummate the Merger or the transactions contemplated by the Merger Agreement.

1.2 Irrevocable Proxy. Solely with respect to the matters described in Section 1.1, for so long as this Agreement has not terminated in accordance with Section 5.1, each Stockholder hereby irrevocably appoints Parent (or any nominee of Parent) as its attorney and proxy with full power of substitution and resubstitution, to the full extent of such Stockholder’s voting rights with respect to such Stockholder’s Voting Shares (which proxy is irrevocable and which appointment is coupled with an interest, including for purposes of Section 212 of the Delaware General Corporation Law) to vote all such Stockholder’s Voting Shares solely on the matters described in Section 1.1, and in accordance therewith. Each Stockholder hereby revokes any proxies previously granted that would otherwise conflict with the proxy contemplated pursuant to this Section 1.2 and agrees to execute any further agreement or form reasonably necessary or appropriate to confirm and effectuate the grant of the proxy contained herein. Such proxy shall automatically terminate upon the valid termination of this Agreement in accordance with Section 5.1.

2. Representations and Warranties of Stockholders. Each Stockholder hereby represents and warrants to Parent as follows:

2.1 Due Organization. Such Stockholder, if a corporation or other entity, has been duly organized, is validly existing and is in good standing under the laws of the state of its formation or organization.

2.2 Power; Due Authorization; Binding Agreement. Such Stockholder has full legal capacity, power and authority to execute and deliver this Agreement, to perform its obligations hereunder and to consummate the transactions contemplated hereby. This Agreement has been duly and validly executed and delivered by such Stockholder and constitutes a valid and binding agreement of such Stockholder, enforceable against Stockholder in accordance with its terms, except to the extent that enforceability may be subject to the effect of any applicable bankruptcy, reorganization, insolvency, moratorium or other similar laws affecting or relating to the enforcement of creditors rights generally and to general principles of equity.

2.3 Ownership of Shares. On the date hereof, the Owned Shares set forth opposite such Stockholder’s name on Attachment A hereto are owned of record or beneficially by such Stockholder in the manner reflected thereon and include all of the Voting Shares owned of record or beneficially by such Stockholder, free and clear of any claims, liens, encumbrances and security interests, except (if applicable) as set forth on Attachment A hereto, which encumbrances or other items do not affect in any respect the ability of such Stockholder to perform such Stockholder’s obligations hereunder. As of the date hereof such Stockholder has, and at all times prior to the valid termination of this Agreement in accordance with Section 5.1 such Stockholder will have (except as otherwise permitted by this Agreement), sole voting power (to the extent such securities have voting power) and sole dispositive power with respect to all of the Owned Shares, except as otherwise reflected on Attachment A.

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2.4 No Conflicts. The execution and delivery of this Agreement by such Stockholder does not, and the performance of the terms of this Agreement by such Stockholder will not, (a) require such Stockholder to obtain the consent or approval of, or make any filing with or notification to, any governmental or regulatory authority, domestic or foreign, (b) require the consent or approval of any other person or entity pursuant to any agreement, obligation or instrument binding on such Stockholder or its properties and assets, (c) conflict with or violate any organizational document or law, rule, regulation, order, judgment or decree applicable to such Stockholder or pursuant to which any of its or its affiliates’ respective properties or assets are bound or (d) violate any other agreement to which such Stockholder or any of its affiliates is a party including, without limitation, any voting agreement, stockholders agreement, irrevocable proxy or voting trust. The Voting Shares are not, with respect to the voting or transfer thereof, subject to any other agreement, including any voting agreement, stockholders agreement, irrevocable proxy or voting trust.

2.5 Acknowledgment. Such Stockholder understands and acknowledges that each of Parent and Merger Sub is entering into the Merger Agreement in reliance upon such Stockholder’s execution, delivery and performance of this Agreement.

3. Representations and Warranties of Parent. Parent hereby represents and warrants to the Stockholders as follows:

3.1 Power; Due Authorization; Binding Agreement. Parent is a corporation duly organized, validly existing and in good standing under the laws of the Commonwealth of Massachusetts. Parent has full corporate power and authority to execute and deliver this Agreement, to perform its obligations hereunder and to consummate the transactions contemplated hereby. The execution and delivery of this Agreement and the consummation by Parent of the transactions contemplated hereby have been duly and validly authorized by all necessary corporate action on the part of Parent, and no other proceedings on the part of Parent are necessary to authorize this Agreement or to consummate the transactions contemplated hereby. This Agreement has been duly and validly executed and delivered by Parent and constitutes a valid and binding agreement of Parent, except that enforceability may be subject to the effect of any applicable bankruptcy, reorganization, insolvency, moratorium or other similar laws affecting or relating to the enforcement of creditors rights generally and to general principles of equity.

3.2 No Conflicts. The execution and delivery of this Agreement by Parent does not, and the performance of the terms of this Agreement by Parent will not, (a) require Parent to obtain the consent or approval of, or make any filing with or notification to, any governmental or regulatory authority, domestic or foreign or (b) conflict with or violate any organizational document or law, rule, regulation, order, judgment or decree applicable to Parent or pursuant to which any of its or its subsidiaries’ respective assets are bound.

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4. Certain Covenants of the Stockholders. Each Stockholder hereby covenants and agrees with Parent as follows:

4.1 Restriction on Transfer, Proxies and Non-Interference. Each Stockholder hereby agrees, while this Agreement is in effect, at any time prior to the Effective Time, and otherwise as is contemplated by the Merger Agreement, not to (a) other than as may be specifically required by a court order, which such Stockholder shall use its reasonable best efforts to avoid (including by offering substitute consideration or property) and provided further that such Stockholder shall use reasonable best efforts to cause any such Voting Shares to be transferred subject to this Agreement, sell, transfer, pledge, encumber (except as set forth on Attachment A or due to this Agreement), assign or otherwise dispose of (including, without limitation, by gift, merger, consolidation or reorganization), or enter into any contract, option or other arrangement or understanding with respect to the sale, transfer, pledge, encumbrance, assignment or other disposition of, or limitation on the voting rights of, any of the Voting Shares (any such action, a “Transfer”), provided that nothing in this Agreement shall prohibit the exercise by such Stockholder of any options to purchase Voting Shares, (b) grant any proxies or powers of attorney, deposit any Voting Shares into a voting trust or enter into a voting agreement with respect to any Voting Shares, (c) take any action that would cause any representation or warranty of such Stockholder contained herein to become untrue or incorrect or have the effect of preventing or disabling Stockholder from performing its obligations under this Agreement, or (d) commit or agree to take any of the foregoing actions. Any action taken in violation of the foregoing sentence shall be null and void ab initio and each Stockholder agrees that any such prohibited action may and should be enjoined. If any involuntary Transfer of any of the Voting Shares shall occur (including, but not limited to, a sale by a Stockholder’s trustee in any bankruptcy, or a sale to a purchaser at any creditor’s or court sale or any sale or transfer by operation of law, including, without limitation, by will or intestacy), the transferee (which term, as used herein, shall include any and all transferees and subsequent transferees of the initial transferee) shall take and hold such Voting Shares subject to all of the restrictions, liabilities and rights under this Agreement, which shall continue in full force and effect until valid termination of this Agreement.

4.2 Additional Shares. Each Stockholder hereby agrees, while this Agreement is in effect, that any shares of Common Stock acquired by such Stockholder after the date hereof shall be subject to the terms of this Agreement as though owned by such Stockholder on the date hereof.

4.3 No Limitations on Actions. Each Stockholder signs this Agreement solely in its capacity as the record and/or beneficial owner, as applicable, of the Owned Shares; any trustee who signs this Agreement on behalf of a Stockholder that is a trust is signing only in his fiduciary capacity and not as an individual; this Agreement shall not limit or otherwise affect the actions of such Stockholder or any affiliate, employee or designee of such Stockholder or any of its affiliates in any other capacity, including such person’s capacity, if any, as an officer of the Company or a member of the board of directors of the Company; and nothing herein shall limit or affect the Company’s rights in connection with the Merger Agreement.

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4.4 No Solicitation. Each Stockholder agrees, while this Agreement is in effect, not to directly or indirectly engage in any activity which would be prohibited pursuant to Section 5.2(a) of the Merger Agreement if engaged in by the Company.

4.5 Disclosure. Each Stockholder hereby permits Parent or the Company to publish and disclose in any proxy materials (including, but not limited to, all documents and schedules filed with the Securities and Exchange Commission) its identity and ownership of shares of Common Stock and the terms of this Agreement.

4.6 Further Assurances. From time to time, at the request of Parent and without further consideration, each Stockholder shall execute and deliver such additional documents and take all such further action as may be necessary or reasonably desirable to consummate and make effective the transactions contemplated by this Agreement.

5. Miscellaneous.

5.1 Termination of this Agreement. This Agreement shall terminate upon the earlier to occur of (i) the termination of the Merger Agreement in accordance with its terms, or (ii) the consummation of the Merger.

5.2 Effect of Termination. In the event of termination of this Agreement pursuant to Section 5.1, this Agreement shall become void and of no effect with no liability on the part of any party hereto; provided, however, no such termination shall relieve any party hereto from any liability for any breach of this Agreement occurring prior to such termination; and provided, further, that upon payment of the Termination Fee (as defined in the Merger Agreement) Stockholder shall have no further liability with respect to this Agreement or the transactions contemplated hereby.

5.3 Non-Survival. The representations and warranties made herein shall not survive the termination of this Agreement.

5.4 Entire Agreement; Assignment. This Agreement constitutes the entire agreement among the parties with respect to the subject matter hereof and supersedes all other prior agreements and understandings, both written and oral, among the parties with respect to the subject matter hereof. Nothing in this Agreement, express or implied, is intended to or shall confer upon any other person or entity any right, benefit or remedy of any nature whatsoever under or by reason of this Agreement. This Agreement shall not be assigned by operation of law or otherwise and shall be binding upon and inure solely to the benefit of each party hereto.

5.5 Amendments. This Agreement may not be modified, amended, altered or supplemented, except upon the execution and delivery of a written agreement executed by each of the parties hereto.

5.6 Notices. Any notice required to be given hereunder shall be sufficient if in writing, and sent by facsimile transmission (provided that any notice received by facsimile transmission or otherwise at the addressee’s location on any Business Day after 5:00 p.m. (addressee’s local time) shall be deemed to have been received at 9:00 a.m. (addressee’s local time) on the next Business Day), by reliable overnight delivery service (with proof of service),

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hand delivery or certified or registered mail (return receipt requested and first-class postage prepaid), addressed as follows:

If to the Stockholders:

Fax:

If to Parent:

Teradyne, Inc.

700 Riverpark Drive

North Reading, Mass. 01864

Attention: Eileen Casal, V.P. & General Counsel

Fax: (978)  ###-###-####

with copy to:

WilmerHale LLP

60 State Street

Boston, Mass 02109

Attention: Jay E. Bothwick, Esq.

Fax: 617 ###-###-####

or to such other address as any party shall specify by written notice so given, and such notice shall be deemed to have been delivered as of the date so telecommunicated, personally delivered or received. Any party to this Agreement may notify any other party of any changes to the address or any of the other details specified in this paragraph; provided, however, that such notification shall only be effective on the date specified in such notice or two Business Days after the notice is given, whichever is later. Rejection or other refusal to accept or the inability to deliver because of changed address of which no notice was given shall be deemed to be receipt of the notice as of the date of such rejection, refusal or inability to deliver.

5.7 Governing Law; Venue.

(a) This Agreement shall be governed by, and construed in accordance with, the Laws of the State of Delaware, without giving effect to conflicts of laws principles that would result in the application of the Law of any other state.

(b) Each of the parties hereto hereby irrevocably and unconditionally submits, for itself and its property, to the exclusive jurisdiction of the Delaware Court of Chancery, or, if no such state court has proper jurisdiction, the Federal court of the United States of America, sitting in Delaware, and any appellate court from any thereof, in any action or proceeding arising out of or relating to this Agreement or the transactions contemplated hereby or for recognition or enforcement of any judgment relating thereto, and each of the parties hereby irrevocably and unconditionally (i) agrees not to commence any such action or proceeding except in such courts; (ii) agrees that any claim in respect of any such action or proceeding may be heard and determined in such Delaware Court of Chancery or, if no such state court has

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proper jurisdiction, then in such Federal court; (iii) waives, to the fullest extent it may legally and effectively do so, any objection which it may now or hereafter have to the laying of venue of any such action or proceeding in any such Delaware Court of Chancery or Federal court; and (iv) waives, to the fullest extent permitted by Law, the defense of an inconvenient forum to the maintenance of such action or proceeding in any such Delaware Court of Chancery or Federal court. Each of the parties hereto agrees that a final judgment in any such action or proceeding shall be conclusive and may be enforced in other jurisdictions by suit on the judgment or in any other manner provided by Law. Each party to this Agreement irrevocably consents to service of process in the manner provided for notices in Section 5.6. Nothing in this Agreement will affect the right of any party to this Agreement to serve process in any other manner permitted by Law. Each party hereto agrees not to commence any legal proceedings relating to or arising out of this Agreement or the Transactions in any jurisdiction or courts other than as provided herein.

5.8 WAIVER OF JURY TRIAL. EACH PARTY HEREBY IRREVOCABLY AND UNCONDITIONALLY WAIVES ANY RIGHT IT MAY HAVE TO A TRIAL BY JURY IN RESPECT OF ANY LITIGATION DIRECTLY OR INDIRECTLY ARISING OUT OF OR RELATING TO THIS AGREEMENT. EACH PARTY CERTIFIES AND ACKNOWLEDGES THAT: (A) NO REPRESENTATIVE, AGENT OR ATTORNEY OF ANY OTHER PARTY HAS REPRESENTED, EXPRESSLY OR OTHERWISE, THAT SUCH OTHER PARTY WOULD NOT, IN THE EVENT OF LITIGATION, SEEK TO ENFORCE SUCH WAIVER; (B) IT UNDERSTANDS AND HAS CONSIDERED THE IMPLICATIONS OF SUCH WAIVER; (C) IT MAKES SUCH WAIVER VOLUNTARILY; AND (D) IT HAS BEEN INDUCED TO ENTER INTO THIS AGREEMENT BY, AMONG OTHER THINGS, THE MUTUAL WAIVERS AND CERTIFICATIONS IN THIS SECTION 5.8.

5.9 Specific Performance. The parties agree that irreparable damage would occur in the event that any of the provisions of this Agreement were not performed in accordance with its specific terms or were otherwise breached. Each Stockholder agrees that, in the event of any breach or threatened breach by such Stockholder of any covenant or obligation contained in this Agreement, Parent shall be entitled (in addition to any other remedy that may be available to it, including monetary damages) to seek and obtain (a) a decree or order of specific performance to enforce the observance and performance of such covenant or obligation, and (b) an injunction restraining such breach or threatened breach. Each Stockholder further agrees that neither Parent nor any other person or entity shall be required to obtain, furnish or post any bond or similar instrument in connection with or as a condition to obtaining any remedy referred to in this Section 5.9, and each Stockholder irrevocably waives any right it may have to require the obtaining, furnishing or posting of any such bond or similar instrument.

5.10 Counterparts. This Agreement may be executed in two or more counterparts, each of which shall be deemed an original but all of which together shall be considered one and the same agreement and shall become effective when counterparts have been signed by each of the parties hereto and delivered to the other parties, it being understood that all parties need not sign the same counterpart. This Agreement may be executed and delivered by facsimile transmission.

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5.11 Descriptive Headings. The descriptive headings used herein are inserted for convenience of reference only and are not intended to be part of or to affect the meaning or interpretation of this Agreement.

5.12 Severability. Any term or provision of this Agreement that is invalid or unenforceable in any situation in any jurisdiction shall not affect the validity or enforceability of the remaining terms and provisions hereof or the validity or enforceability of the offending term or provision in any other situation or in any other jurisdiction. If the final judgment of a court of competent jurisdiction declares that any term or provision hereof is invalid or unenforceable, the parties hereto agree that the court making such determination shall have the power to limit the term or provision, to delete specific words or phrases, or to replace any invalid or unenforceable term or provision with a term or provision that is valid and enforceable and that comes closest to expressing the intention of the invalid or unenforceable term or provision, and this Agreement shall be enforceable as so modified. In the event such court does not exercise the power granted to it in the prior sentence, the parties hereto agree to replace such invalid or unenforceable term or provision with a valid and enforceable term or provision that will achieve, to the extent possible, the economic, business and other purposes of such invalid or unenforceable term.

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IN WITNESS WHEREOF, the parties hereto have caused this Stockholders’ Agreement to be duly executed as of the day and year first above written.

ATTACHMENT A

Details of Ownership